Wireless communication apparatus

ABSTRACT

A wireless communication apparatus supports at least a second wireless communication scheme between a first wireless communication scheme and the second wireless communication scheme. The first wireless communication scheme requires that a wireless medium is determined to be busy when a reception level is equal to or greater than a minimum reception sensitivity level of a physical scheme. The apparatus includes a first processing unit and a second processing unit. The first processing unit is configured to set a value lower than a maximum transmission power of the first wireless communication scheme, for a maximum transmission power of the second wireless communication scheme and set a value greater than the minimum reception sensitivity level of the physical scheme, for a carrier sense level, when the second wireless communication scheme is used. The second processing unit is configured to carry out carrier sense using the carrier sense level.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional of U.S. application Ser. No. 13/223,587, filed Sep.1, 2011, which is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2011-019059, filed Jan. 31, 2011,the entire contents of both of which are incorporated herein byreference.

FIELD

Embodiments described herein relate generally to wireless communication.

BACKGROUND

As a wireless communication scheme based on carrier sense, for example,IEEE 802.11 is known. In IEEE 802.11, a carrier sense level is uniquelydetermined for each physical scheme. Thus, according to IEEE 802.11, aplurality of wireless communication apparatuses using the same physicalscheme can share the same wireless medium for coexistence.

However, problems may occur if the wireless communication apparatus(referred to as a first wireless communication apparatus in BACKGROUNDfor convenience) controls the maximum transmission power based on awireless communication scheme (which is based on carrier sense), forexample, IEEE 802.11, to implement close proximity wirelesscommunication with a communication range limited to the order of, forexample, several centimeters. Specifically, the equal coexistencebetween the first wireless communication apparatus and another wirelesscommunication apparatus using the normal maximum transmission power (inBACKGROUND, this wireless communication apparatus is referred to as asecond wireless communication apparatus for convenience) is difficult ifthe second wireless communication apparatus uses the same wirelessmedium as that for the first wireless communication apparatus and if thefirst wireless communication apparatus is present within thecommunication range of the second wireless communication apparatus. Thefollowing situation may occur, for example: signals transmitted by thefirst wireless communication apparatus fail to reach the carrier senselevel of the second wireless communication apparatus; however, signalstransmitted by the second wireless communication apparatus reach thecarrier sense level of the second wireless communication apparatus.Hence, the second wireless communication apparatus can transmit signalsregardless of the status of transmissions from the first wirelesscommunication apparatus. However, the first wireless communicationapparatus is prevented from transmitting signals depending on the statusof transmissions from the second wireless communication apparatus. Thatis, the first wireless communication apparatus is in an inferiorposition compared to the second wireless communication apparatus.

Furthermore, the conventional wireless communication scheme based oncarrier sense assumes that a plurality of wireless communicationapparatuses communicate with one another. Moreover, the wirelesscommunication scheme is designed based on the policy that even if acommunication link is degraded, an attempt is made to maintain thecommunication link. On the other hand, in the close proximitycommunication, the communication among a plurality of wirelesscommunication apparatuses is not always necessary, and point-to-pointcommunication often has to be only implemented. Moreover, requirementspecifications for the close proximity communication include a reductionin the time required until data exchange is started and distinctdisconnection of a communication link when a communication distancebecomes longer than a certain level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a wireless communicationapparatus according to a first embodiment;

FIG. 2 is a diagram illustrating a carrier sense level used by awireless communication apparatus based on a close proximity scheme;

FIG. 3 is a block diagram illustrating a wireless communicationapparatus according to a second embodiment;

FIG. 4 is a block diagram illustrating a wireless communicationapparatus according to a third embodiment;

FIG. 5 is a diagram illustrating a schedule for a Beacon Interval; and

FIG. 6 is a table illustrating parameters provided in anMLME-SCAN.request primitive based on IEEE 802.11.

DETAILED DESCRIPTION

Embodiments will be described below with reference to the drawings. Inthe embodiments, elements that are the same or similar to describedelements are denoted by the same or similar reference numerals.Duplicate descriptions are basically omitted.

According to embodiments, a wireless communication apparatus supports atleast a second wireless communication scheme between a first wirelesscommunication scheme and the second wireless communication scheme. Thefirst wireless communication scheme requires that a wireless medium isdetermined to be busy when a reception level is equal to or greater thana minimum reception sensitivity level of a physical scheme. Theapparatus includes a first processing unit, a second processing unit anda third processing unit. The first processing unit is configured to seta value lower than a maximum transmission power of the first wirelesscommunication scheme, for a maximum transmission power of the secondwireless communication scheme and set a value greater than the minimumreception sensitivity level of the physical scheme, for a carrier senselevel, when the second wireless communication scheme is used. The secondprocessing unit is configured to carry out carrier sense using thecarrier sense level. The third processing unit is configured to controltransmission and reception of a signal via the second processing unit.

The embodiments will be described below assuming an IEEE 802.11 wirelessLAN as an example of the wireless communication scheme based on carriersense. Of course, the embodiments can be applied to other wirelesscommunication schemes.

IEEE 802.11 deals with a plurality of frequency bands. In IEEE 802.11, aphysical layer (PHYsical; PHY) specification is provided for each of theplurality of frequency bands. A medium access control (MAC) layerspecification is provided as a higher layer specification to the PHYspecification.

For example, 802.11a specifies a 5-GHz band, 802.11g specifies a 2.4-GHzband, and 802.11n specifies the 2.4-GHz band and the 5-GHz band.Moreover, 802.11ad, which is under the standardization process, is tospecify a 60-GHz band (millimeter-wave band).

These PHY specifications include specifications for carrier senselevels. Upon receiving power that is equal to or greater than aspecified carrier sense level, a wireless communication apparatus isrequired to determine that a medium (Clear Channel Assessment; CCA) isbusy. More specifically, upon receiving a supported PHY signal which thewireless communication apparatus supports, the wireless communicationapparatus is required to determine that the medium (CCA) is busyprovided that the reception level (Receive Signal Strength Indicator;RSSI) of the signal is equal to or greater than the minimum receivingsensitivity according to the PHY scheme. Otherwise (for example, if thewireless communication apparatus receives a signal not known to be basedon the supported PHY scheme, a signal based on a PHY scheme differentfrom the supported one, or simply noise), the wireless communicationapparatus is required to determine that the medium (CCA) is busyprovided that the reception level is equal to or greater than theabove-described minimum reception sensitivity plus a fixed value.According to the IEEE 802.11 wireless LAN, the fixed value is basicallyspecified to be 20 dB. Adjustment of the carrier sense level will bedescribed below, and in the description, the carrier sense level refersto the carrier sense level used when a signal based on the supported PHYscheme is received (that is, the carrier sense level to which the fixedvalue is not added).

Now, a technique to detect the PHY scheme will be described. A PHYscheme used to transmit a PHY packet is described in a PHY header of thePHY packet. Thus, if the reception signal is a PHY packet, the wirelesscommunication apparatus can refer to the PHY header to determine whetheror not the received signal is based on the supported PHY scheme.

(First Embodiment)

As shown in FIG. 1, a wireless communication apparatus according to afirst embodiment includes a higher layer processing unit 100, a MACprocessing unit 10, a PHY processing unit 40, a frequency conversioncircuit 50, and an antenna 60.

The higher layer processing unit 100 carries out processing for thehigher layer above the MAC layer. The high layer processing unit canexchange signals with the MAC processing unit 10.

The MAC processing unit 10 carries out processing for the MAC layer. Asdescribed above, the MAC processing unit 10 can exchange signals withthe higher layer processing unit 100. The MAC processing unit 10 canfurther exchange signals with the PHY processing unit 40. The MACprocessing unit 10 includes a reception processing unit 20 and atransmission processing unit 30.

The PHY processing unit 40 carries out processing for the PHY layer. Asdescribed above, the PHY processing unit 40 can exchange signals withthe MAC processing unit 10. The PHY processing unit 40 is connected tothe antenna 60 via the frequency conversion circuit 50. The frequencyconversion circuit 50 carries out up-conversion/down-conversion toexchange signals.

In FIG. 1 or other drawings, the single antenna 60 is shown, but ofcourse, a plurality of antennas 60 may be provided. Furthermore, aplurality of different PHY processing units 40 may be provided, andreception processing units 20 and transmission processing units 30corresponding to the respective PHY processing units 40 may be provided.Moreover, a common processing unit covering the plurality of PHYprocessing units 40 may be provided.

Furthermore, the wireless communication apparatus according to thepresent embodiment includes the antenna 60 as a component as shown inFIG. 1 (the wireless communication apparatus is integrated with theantenna 60). Thus, the implementation area of the antenna 60 can bereduced. Moreover, in the wireless communication apparatus according tothe present embodiment, the reception processing unit 20 and thetransmission processing unit 30 share the antenna 60 as shown in FIG. 1.The antenna shared by the reception processing unit 20 and thetransmission processing unit 30 allows compact implementation of thewireless communication apparatus in FIG. 1. Of course, the wirelesscommunication apparatus according to the present embodiment may beconfigured differently from the one illustrated in FIG. 1.

When transmitting a signal, the PHY processing unit 40 receives a MACframe from the transmission processing unit 30. The PHY processing unit40 carries out processing such as encoding on the MAC frame to convertthe MAC frame into a PHY packet. The frequency conversion circuit 50converts the PHY packet into a wireless signal on a required frequencyband (for example, 60-GHz millimeter-wave band). The antenna 60 radiatesthe wireless signal resulting from the frequency conversion. During thesignal transmission, the PHY processing unit 40 outputs a signalindicating that the medium is busy, to the MAC processing unit 10 (moreprecisely, to the reception processing unit 20).

When receiving a signal, the frequency conversion circuit 50 converts awireless signal received by the antenna 60 into a signal on a requiredfrequency band (a baseband that can be processed by the PHY processingunit 40). The PHY processing unit 40 receives the reception signal onthe baseband to detect the reception level of the signal, whiledetermining the PHY scheme of the signal. The PHY processing unit 40selects a carrier sense level in accordance with the PHY scheme. The PHYprocessing unit 40 compares the selected carrier sense level with thereception level. If the reception level is equal to or greater than theselected carrier sense level, the PHY processing unit 40 outputs asignal indicating that the medium (CCA) is busy, to the MAC processingunit 10 (more precisely, the reception processing unit 20). Otherwise,the PHY processing unit 40 outputs a signal indicating that the medium(CCA) is idle, to the MAC processing unit 10 (more precisely, thereception processing unit 20). If the received signal is based on theappropriate PHY scheme (that is, the PHY scheme which the wirelesscommunication apparatus supports), the PHY processing unit 40 carriesout a decoding process, a process of removing a preamble and a PHYheader, and the like to extract a payload. The PHY processing unit 40passes the payload to the reception processing unit 20 as a MAC frame.Moreover, before passing the MAC frame to the reception processing unit20, the PHY processing unit 40 notifies the reception processing unit 20that reception of a PHY packet is to start. After passing the MAC frameto the reception processing unit 20, the PHY processing unit 40 notifiesthe reception processing unit 20 that the reception of the PHY packethas ended. Furthermore, if the received PHY packet is normal (no erroris detected), the PHY processing unit 40 notifies the receptionprocessing unit 20 that the reception of the PHY packet has ended, andpasses a signal indicating that the medium is idle, to the receptionprocessing unit 20. When detecting an error in the received packet, thePHY processing unit 40 notifies the reception processing unit 20 thatthe error has been detected.

The MAC processing unit 10 deals with three types of MAC frames; a dataframe, a control frame, and a management frame, and carries out varioustypes of processing specified for the MAC layer. Now, the three types ofMAC frames will be described.

The management frame is used to manage communication links with otherwireless communication apparatuses. For example, the management frameincludes a beacon frame used to report group attribute andsynchronization information required to form a wireless communicationgroup that is a basic service set (BSS) based on IEEE 802.11, and framesexchanged with other wireless communication apparatuses forauthentication or establishment of communication links.

The data frame is used to transmit data to another wirelesscommunication apparatus with a communication link with this wirelesscommunication apparatus established. For example, a user manipulates arelevant application to generate data in the wireless communicationapparatus in FIG. 1. The data is carried by the data frame.Specifically, the generated data is passed from the higher layerprocessing unit 100 to the transmission processing unit 30. Duringtransmission, the data is carried in a frame body field of the dataframe as a payload. Furthermore, upon receiving the data frame, thereception processing unit 20 extracts and processes information in theframe data field as data. The reception processing unit 20 then passesthe processed information to the higher layer processing unit 100. Thisallows the application to perform an operation such as data write orreproduction.

The control frame is used for control during transmission and reception(exchange) of the management and data frames with another wirelesscommunication apparatus. The control frame includes an RTS (Request ToSend) frame and a CTS (Clear To Send) frame which are exchanged withanother wireless communication apparatus in order to reserve the mediumbefore starting to exchange the management and data frames. Furthermore,the control frame includes an ACK (Acknowledgement) frame and a BA(Block Ack) frame which are transmitted for confirmation of delivery ofthe received management and data frames.

The MAC processing unit 10 needs to acquire an access right(transmission right) on the medium before transmitting the MAC frame.The transmission processing unit 30 adjusts a transmission timing basedon carrier sense information (described below) from the receptionprocessing unit 20. The transmission processing unit 30 gives atransmission instruction to and passes the MAC frame to the PHYprocessing unit 40 in accordance with the transmission timing. Inaddition to giving the transmission instruction, the transmissionprocessing unit 30 may indicate to the PHY processing unit 40 amodulation scheme and a coding scheme used for the transmission.Further, the transmission processing unit 30 may indicate transmissionpower to the PHY processing unit 40. Once acquiring the access right,the MAC processing unit 10 can consecutively exchange MAC frames withanother wireless communication apparatus, while a media occupation time,QoS (Quality of Service) attributes and the like limited. For example,the access right is acquired when the wireless communication apparatustransmits a predetermined frame and correctly receives a response framefrom another wireless communication apparatus. When the predeterminedframe is received by another wireless communication apparatus, thiswireless communication apparatus transmits the response frame after aminimum frame interval time (Short Interval Frame Space) elapses, forexample.

The reception processing unit 20 manages carrier sense information. Thecarrier sense information includes both physical carrier senseinformation relating to the busy/idle state of the medium according tothe input by the PHY processing unit 40 and virtual carrier senseinformation based on a medium reservation time described in the receivedframe. If one of these pieces of information indicates the busy state,signal transmissions are inhibited during the state. In IEEE 802.11, themedium reservation time is described in what is called a duration/IDfield in the MAC header. Upon receiving a MAC frame destined for anotherwireless communication apparatus (not for the present wirelesscommunication apparatus), the MAC processing unit 10 determines that themedium is virtually busy for the medium reservation time from the end ofthe PHY packet containing the MAC frame. A mechanism for virtuallydetermining the medium to be busy or the period when the medium isvirtually busy is referred to as the NAV (Network Allocation Vector).

As described below, the wireless communication apparatus according tothe present embodiment is based on a normal wireless communicationscheme using a carrier sense (CCA) in accordance with the minimumreception sensitivity level of the above-described PHY scheme, torealize a close proximity communication scheme that can coexist with thenormal wireless communication scheme. The normal wireless communicationscheme is hereinafter referred to as a normal scheme for convenience (ormay be referred to as a non-close proximity scheme). The close proximitywireless communication scheme that can coexist with the normal wirelesscommunication scheme is referred to as a close proximity scheme.

As described below, the wireless communication apparatus according tothe present embodiment may support a scheme for a particular frequencyband or may be hybrid and support a scheme for a plurality of frequencybands. Moreover, the wireless communication apparatus according to thepresent embodiment may support both the close proximity scheme and thenormal scheme (for example, wireless LAN). In the description below, thewireless communication apparatus according to the present embodiment isassumed to support at least the close proximity scheme based on thenormal wireless LAN scheme. Here, the close proximity scheme is assumedto be such that the communication range is limited to of the order ofseveral centimeters (for example, 3 cm) and that communication isenabled within the communication range.

The wireless communication apparatus controls the maximum transmissionpower in order to limit the communication range. For example, when thewireless communication apparatus uses a millimeter-wave band, it can beassumed that; a propagation loss is a free space propagation loss+10 dB,and an antenna gain is 0 dB for both transmission and reception. Here,the wireless communication apparatus selects a predetermined modulationand coding scheme (MCS) with the lowest reception sensitivity level inthe system to transmit a basic management frame, for example, a beacon.The MCS is referred to as MCS0 and its reception sensitivity level isassumed to be −78 dBm. On the other hand, the wireless communicationapparatus selects one of MCS1 to MCS12 involving greater receptionsensitivity levels than MCS0 to transmit other frames including the dataframe. Among MCS1 to MCS12, MCS1 is assumed to have the minimumreception sensitivity level of −68 dB. Furthermore, MCS0 is assumed tobe distinguished from MCS1 to MCS 12 based on a difference in PHYscheme.

For example, it is assumed that if the wireless communication apparatusselects MCS0, the transmission power needs to be −30 dBm in order to setthe reception level at a distance of 3 cm from the transmission sourceto −78 dBm. On the other hand, it is assumed that if the wirelesscommunication apparatus selects MCS4, the transmission power needs to be−16 dBm in order to set the reception level at a distance of 3 cm fromthe transmission source to −64 dBm (the reception sensitivity level ofMCS4, 31 64 dBm, is greater than the reception sensitivity level ofMCS0, −78 dBm, by 14 dB, and the transmission power needs to beincreased by 14 dB). When the transmission power is −16 dBm, thedistance at which the carrier sense (CCA) indicates the busy state, thatis, the distance at which the reception level exceeds the receptionsensitivity level of MCS1, −68 dBm, is for example, 5 cm. That is,compared to the case when the wireless communication apparatus usesMCS0, the distance at which the carrier sense (CCA) indicates busyincreases. If the minimum transmission rate within a predeterminedcommunication range is required, the wireless communication apparatusmay select one of the MCSs which can achieve the transmission rate to beachieved and set the maximum transmission power such that the minimumreception sensitivity is obtained at the edge of the predeterminedcommunication range. Then, the wireless communication apparatus mayenable this MCS or any other MCS with a higher transmission rate to beexclusively selected and carry out transmission with transmission powerequal to or lower than the set maximum transmission power. That is, themaximum transmission power of the wireless communication apparatus islower than that for the normal scheme.

The transmission power based on the normal scheme is normally betweenabout 0 dBm and several tens of dBm. That is, the above-describedcontrolled transmission power is lower than that for the normal schemeby about several tens of dBm as exemplified for MCS0 and MCS1 to MCS4.

Furthermore, the scheme in which the communication range is limited bycontrolling the maximum transmission power is in an inferior positioncompared to the normal scheme under coexistence. For example, it isassumed that two wireless communication apparatuses are arranged (in thepresent embodiment, one of the wireless communication apparatuses isreferred to as a first wireless communication apparatus and the other isreferred to as a second wireless communication apparatus); the secondwireless communication apparatus transmits the beacon frame at atransmission power of 10 dBm, and the first wireless communicationapparatus transmits the beacon frame with the maximum transmission powerlimited to −30 dBm. When the second wireless communication apparatusselects MCS0 and transmits the beacon frame at a transmission power of10 dBm, the reception level at a distance of 3 m from the transmissionsource is equal to the reception sensitivity level of −78 dBm. Thus, ifthe distance between the first wireless communication apparatus and thesecond wireless communication apparatus is equal to or shorter than 3 m,the reception level at the first wireless communication apparatus isequal to or greater than −78 dBm. That is, the first wirelesscommunication apparatus determines that CCA is busy. On the other hand,when the first wireless communication apparatus selects MCS0 andtransmits the beacon frame at a transmission power of −30 dBm, thereception level at a distance of 3 cm from the transmission source isequal to the reception sensitivity level of −78 dBm. Hence, if thedistance between the second wireless communication apparatus and thefirst wireless communication apparatus is longer than 3 cm, thereception level at the second wireless communication apparatus is lessthan −78 dBm. That is, the second wireless communication apparatusdetermines that CCA is idle. Consequently, while the second wirelesscommunication apparatus is transmitting a signal, the first wirelesscommunication apparatus detects interference and cannot transmit itssignal. On the other hand, while the first wireless communicationapparatus is transmitting a signal, the second wireless communicationapparatus detects no interference and can thus transmit its signal.Therefore, it is more difficult for the first wireless communicationapparatus to acquire the transmission right than for the second wirelesscommunication apparatus. In this sense, the first wireless communicationapparatus is inferior to the second wireless communication apparatus.

Thus, the wireless communication apparatus according to the presentembodiment implements the close proximity scheme described below. Theclose proximity scheme, for example, limits the maximum transmissionpower, while using a higher carrier sense level than the normal scheme.That is, when the wireless communication apparatus based on the closeproximity scheme is located away from a wireless communication apparatusbased on the normal scheme to the extent that the wireless communicationapparatus based on the close proximity scheme does not interfere withthe wireless communication apparatus based on the normal scheme (whenthe wireless communication apparatus based on the close proximity schemetransmits a signal, the wireless communication apparatus based on thenormal scheme does not determine that the CCA is busy), even uponreceiving the signal from the wireless communication apparatus based onthe normal scheme, the wireless communication apparatus based on theclose proximity scheme does not detect it as interference. Specifically,the PHY processing unit 40 avoids determining that CCA is busy andproviding the corresponding notification to the MAC processing unit 10(more precisely, the reception processing unit 20). The close proximityscheme is assumed to use the same PHY scheme (the same PHY packet formatand the same MCS set) as that of the normal scheme. Furthermore, it isassumed that the close proximity scheme is required to achieve thetransmission rate for MCS0 at a distance of 3 cm from the transmissionsource.

Now, the carrier sense level used by the wireless communicationapparatus based on the close proximity scheme will be described withreference to FIG. 2. It is assumed that the wireless communicationapparatus based on the normal scheme selects MCS0 to transmit signals ata transmission power of 10 dBm, whereas the wireless communicationapparatus based on the close proximity scheme selects MCS0 to transmitsignals at a transmission power of 0 dBm (that is, the maximumtransmission power of the close proximity scheme is limited to 0 dBm).Moreover, it is assumed that the propagation loss is the free spacepropagation loss+10 dB and that the antenna gain is 0 dB for bothtransmission and reception. In FIG. 2, the wireless communicationapparatuses are denoted as STA (station). When the distance between thewireless communication apparatus based on the normal scheme and thewireless communication apparatus based on the close proximity scheme is1 m, a signal transmitted by the wireless communication apparatus basedon the close proximity scheme using the selected MCS0 is received by thewireless communication apparatus based on the normal scheme at areception level of −78 dBm. Thus, if the two wireless communicationapparatuses are at a distance of longer than 1 m from each other, thewireless communication apparatus based on the normal scheme does notdetermine that CCA is busy by the signal from the wireless communicationapparatus based on the close proximity scheme. Thus the wirelesscommunication apparatus based on the normal scheme can transmit signals.

Now, the carrier sense level used by the wireless communicationapparatus based on the close proximity scheme will be discussed; thecarrier sense level is adjusted to allow the wireless communicationapparatus based on the close proximity scheme and the wirelesscommunication apparatus based on the normal scheme to coexist equallywhile these wireless communication apparatuses locate at a distance oflonger than 1 m from each other. When the distance between the wirelesscommunication apparatuses is 1 m, a signal transmitted by the wirelesscommunication apparatus based on the normal scheme by selectively usingMCS0 is received by the wireless communication apparatus based on theclose proximity scheme at a reception level of −68 dBm. The receptionlevel of −68 dBm is greater than the reception level required for MCS0,that is, −78 dBm. As is apparent from the above-described example, for asignal transmitted at a transmission power of 10 dBm by selectivelyusing MCS0, the reception sensitivity level of −78 dBm is only achievedat a distance of 3 m from the transmission source. Hence, even if thewireless communication apparatus based on the close proximity scheme islocated at a distance of slightly longer than 1 m from the wirelesscommunication apparatus based on the normal scheme, the wirelesscommunication apparatus based on the close proximity scheme determinesthat CCA is busy based on the signal from the wireless communicationapparatus based on the normal scheme because the reception level in thiscase is greater than −78 dBm.

Thus, the wireless communication apparatus according to the presentembodiment sets the carrier sense level to, for example, greater than−68 dBm so as to avoid determining that CCA is busy even in theabove-described circumstances. It is assumed that the maximumcommunication range for the close proximity scheme is 3 cm and that fora signal transmitted at a transmission power of 0 dBm by selectivelyusing MCS0, the reception level is −48 dBm at a distance of 3 cm fromthe transmission source. Under these conditions, the wirelesscommunication apparatus according to the present embodiment sets thecarrier sense level for MCS0 to −48 dBm. That is, the PHY processingunit 40 determines that CCA is busy when the reception level is equal toor greater than −48 dBm and the PHY processing unit 40 notifies the MACprocessing unit 10 that CCA is busy. Then, the PHY processing unit 40extracts a payload from a PHY packet successively received when thereception level is equal to or greater than −48 dBm. The PHY processingunit 40 then passes the payload to the MAC processing unit 10 as a MACframe.

Even if the reception level is somewhat less than −48 dBm, the wirelesscommunication apparatus may successfully receive the correspondingsignal because this reception level is sufficiently high compared to thereception performance (reception sensitivity) of the wirelesscommunication apparatus. However, when the reception level is less than−48 dBm, the PHY processing unit 40 avoids determining that CCA is busy(that is, determines that CCA is idle) and notifying the MAC processingunit 10 that CCA is busy. Furthermore, the PHY processing unit 40 avoidspassing the payload from the PHY packet to the MAC processing unit 10.Hence, the wireless communication apparatus according to the presentembodiment also carries out the above-described virtual carrier sense atthe MAC level based on the MAC frame from the PHY packet successfullyreceived at a reception level equal to or greater than −48 dBm.

Operations performed to receive a PHY packet using MCS1 or any higherMCS will be discussed.

First, a case where MCS0 and the rest of MCS1 to MCS12 are categorizedinto the same PHY scheme will be discussed. In this case, the wirelesscommunication apparatus may use −48 dBm as a carrier sense level for allMCSs. That is, the PHY processing unit 40 may determine that CCA is busyif the reception level for any MCS is equal to or greater than −48 dBmand otherwise determine that CCA is idle.

Next, a case where MCS0 and the rest of MCS1 to MCS12 are categorizedinto different PHY schemes will be discussed. As described above, whenthe minimum reception sensitivity level of MCS1, −68 dBm, is used as acarrier sense level for the normal scheme, the difference in carriersense level between MCS0 and MCS1 for the normal scheme is 10 dB.However, as described above, if the transmission power is limited to 0dBm, the reception level is −48 dBm (that is, the carrier sense levelfor MCS0 in the close proximity scheme) at a distance of 3 cm from thetransmission source. This reception level is as much as 20 dB greaterthan the minimum reception sensitivity level of MCS1 based on the normalscheme. Hence, in the close proximity scheme, the wireless communicationapparatus can sufficiently receive MCS1 signals even though the carriersense level for MCS1 is set to −48 dBm, which is the same value as thatfor MCS0.

That is, the wireless communication apparatus can receive signals basedon a given MCS if the difference (for example, 10 dB) between theminimum reception sensitivity (for example, −78 dBm) for the MCS withthe minimum transmission rate (for example, MCS0) in the close proximityscheme and the minimum reception sensitivity (for example, −68 dBm) fora given MCS (for example, MCS1) is equal to or smaller than thedifference (for example, 30 dBm) between the carrier sense level (forexample, −78 dBm) for the normal scheme and the carrier sense level (forexample, −48 dBm) for the close proximity scheme. On the other hand, ifthe difference between the minimum reception sensitivity level of theMCS with the minimum transmission rate in the close proximity scheme andthe minimum reception sensitivity level of the given MCS is greater thanthe difference in carrier sense level between the normal scheme and theclose proximity scheme, the communication range for the given MCS isnarrower than the communication range (for example, 3 cm) for the MCSwith the minimum transmission rate. A decrease in communication rangewith increasing transmission rate for the MCS is similar to what iscalled link adaptation and thus poses no problem. Thus, even if MCS0 andthe rest of MCS1 to MCS12 are categorized into different PHY schemes,the wireless communication apparatus may use a single carrier senselevel (for example, −48 dBm) for the close proximity scheme. That is,the PHY processing unit 40 may determine that CCA is busy if thereception level for any MCS is equal to or greater than −48 dBm andotherwise determine that CCA is idle.

Furthermore, as described above, upon receiving a signal other thanthose based on the supported PHY scheme, the wireless communicationapparatus uses the minimum reception sensitivity plus 20 dB as a carriersense level. However, even the addition of 20 dB to the minimumreception sensitivity (−68 dBm) for MCS1 does not result in a carriersense level greater than that for the close proximity level, −48 dBm.Hence, even with the above-described fixed value taken into account, thewireless communication apparatus may use the single carrier sense level(for example, −48 dBm) for the close proximity scheme. That is, the PHYprocessing unit 40 may determine that CCA is busy if the reception levelfor any MCS is equal to or greater than −48 dBm and otherwise determinethat CCA is idle.

One of the reasons why in the normal scheme, MCS0 and the rest of MCS1to MCS12 are categorized into different PHY schemes is as follows: ingeneral, in millimeter-wave band communication, a PHY scheme for dataframe exchange (that is, any of MCS1 to MCS12 ) utilizes a high antennagain (directionality). Here, MCS0 is designed as a PHY scheme covering awide communication range in order to allow surrounding wirelesscommunication apparatuses to know the presence of one wirelesscommunication group. Specifically, MCS0 is designed as a robust PHYscheme with the widest directionality range (that is, quasi-omnidirectionality) achievable in the millimeter-wave band in a practicalsense. On the other hand, MCS1 to MCS12 are designed according to thepolicy that the directionality is actively utilized to allow wirelesscommunication apparatuses to actually exchange data frames.Specifically, MCS1 to MCS12 are designed as a PHY scheme in whichtraining on directionality is carried out to increase the antenna again,thus providing a high transmission rate.

On the other hand, for the close proximity scheme, discovery of acommunication peer, establishment of a communication link, and exchangeof data frames often need to be carried out in a short time. Thus, a PHYscheme may be designed under the policy that the directionality is notnecessarily actively utilized. That is, the close proximity scheme maynot be designed to transmit management frames such as the beacon framein accordance with MCS0 , in contrast to the normal scheme, but may bedesigned to transmit management frames in accordance with any of MCS1 toMCS12 as in the case of data frames. In this case, the close proximityscheme does not use MCS0 but one PHY scheme (one of MCS1 to MCS12 ).However, the above description may be replaced with the phrase “theclose proximity scheme is required to achieve the transmission rate forMCS1 at a distance of 3 cm from the transmission source”.

Moreover, the close proximity scheme may be designed to be used only forsome of MCS1 to MCS12 depending on the requirement for the transmissionrate. Also in this case, the wireless communication apparatus mayprovide one carrier sense level greater than the minimum receptionsensitivity in the PHY schemes used and determine the busy/idle state ofCCA based on the value of the carrier sense level.

As described above, the wireless communication apparatus according tothe first embodiment carries out close proximity wireless communicationin accordance with the close proximity scheme using the maximumtransmission power limited to a small value compared to the normalscheme (the maximum transmission power is, for example, 10 dBm for thenormal scheme and 0 dBm for the close proximity scheme) as well as acarrier sense level greater than that for the normal scheme (the carriersense level is, for example, −78 dBm for the normal scheme and −48 dBmfor the close proximity scheme). Thus, the wireless communicationapparatus according to the present embodiment makes the basis fordetection of interference with signals from another wirelesscommunication apparatus stricter (more insensitive) than that for thenormal scheme. This prevents the wireless communication apparatus basedon the close proximity scheme from being inferior to the wirelesscommunication apparatus based on the normal scheme. That is, thewireless communication apparatus based on the normal scheme and thewireless communication apparatus based on the close proximity scheme cancoexist equally.

As is apparent from the above discussion, the following occurs if thewireless communication apparatus based on the normal scheme is arrangedvery close to the wireless communication apparatus using the closeproximity scheme. Even when the wireless communication apparatus is setto have the higher carrier sense level for the close proximity scheme,the wireless communication apparatus still detects interference. In thiscase, the wireless communication apparatuses are desirably shifted toanother frequency channel with no interference. This also applies to acase where after the wireless communication apparatus based on the closeproximity scheme starts wireless communication, the wirelesscommunication apparatus based on the normal scheme starts wirelesscommunication nearby. Of course, the same also applies to a case wherewireless communication apparatuses using the close proximity scheme andbelonging to different BSSs are located extremely close to each other.In short, these phenomena are similar to the interference betweenwireless communication apparatuses using the normal scheme and belongingto different BSSs (that is, wireless communication groups). Thus, ameasure similar to that taken for the interference between wirelesscommunication apparatuses using the normal scheme and belonging todifferent BSSs may be taken for the phenomena. That is, detection ofinterference in the normal scheme, a change in the frequency channel ofa BSS, and the like may be appropriately applied.

Alternatively, the carrier sense level and maximum transmission power ofthe close proximity scheme may be set by, for example, a functional unit(for example, a MAC/PHY management unit 70 described below) to controlthe MAC processing unit 10 or the MAC processing unit 10 with a part ofthe functional unit incorporated therein. Alternatively, the carriersense level and maximum transmission power of the close proximity schememay be set automatically or in accordance with an instruction from aperson such as a user if the close proximity scheme is used.

(Second Embodiment)

A wireless communication apparatus according to a second embodimentsupplements the wireless communication apparatus according to the firstembodiment described above. The wireless communication apparatusaccording to the present embodiment supports both the above-describedclose proximity scheme and normal scheme, and can operate in accordancewith one of the schemes selected as required. The wireless communicationapparatus according to the present embodiment selects the normal schemeby default.

As illustrated in FIG. 3, the wireless communication apparatus accordingto the present embodiment includes a higher layer processing unit 100, aMAC processing unit 10, a PHY processing unit 40, a frequency conversioncircuit 50, an antenna 60, and a MAC/PHY management unit 70.

The MAC/PHY management unit 70 is connected to each of the higher layerprocessing unit 100, the MAC processing unit 10 (more specifically, areception processing unit 20 and a transmission processing unit 30), andthe PHY processing unit 40. The MAC/PHY management unit 70 manages MACand PHY operations in the wireless communication apparatus.

The MAC/PHY management unit 70 corresponds to SME (Station ManagementEntity) in IEEE 802.11 wireless LAN. The interface between the MAC/PHYmanagement unit 70 and the MAC processing unit 10 corresponds to MLMESAP (MAC subLayer Management Entity Service Access Point) in IEEE 802.11wireless LAN. The interface between the MAC/PHY management unit 70 andthe PHY processing unit 40 corresponds to PLME SAP (Physical LayerManagement Entity Service Access Point) in IEEE 802.11 wireless LAN.

In FIG. 3, the MAC/PHY management unit 70 is shown to include afunctional unit for MAC management and a functional unit for PHYmanagement which are integrated with each other. However, the MAC/PHYmanagement unit 70 may be implemented in a different manner providedthat the MAC/PHY management unit 70 can achieve the followingoperations.

The MAC/PHY management unit 70 holds a Management Information Base(MIB). The MIB holds various types of information in order to implementthe close proximity scheme.

For example, the MIB holds an attribute indicating whether or not thewireless communication apparatus operates in accordance with the closeproximity scheme (whether or not the wireless communication apparatusselects an attribute for the close proximity scheme). Such an attributecan be named, for example, dot11CloseProximityCommunicationEnabled. ATRUE value is set for the attribute when the wireless communicationapparatus uses the close proximity scheme. A FALSE value is set for theattribute when the wireless communication apparatus uses the normalscheme. As described above, the attribute is set to FALSE (normalscheme) by default.

For example, when the user selects an application for the closeproximity scheme, the MAC/PHY management unit 70 is provided, via thehigher layer processing unit 100, with an instruction to rewrite thevalue of dot11CloseProximityCommunicationEnabled attribute to TRUE. Inaccordance with the instruction, the MAC/PHY management unit 70 rewritesthe value of dot11CloseProximityCommunicationEnabled attribute to TRUE.Alternatively, if the higher layer processing unit 100 selects the closeproximity scheme based on a certain algorithm, the rewrite instructionmay be provided to the MAC/PHY management unit 70. Furthermore, if theuser selects the close proximity scheme, the higher layer processingunit 100 may provide the rewrite instruction to the MAC/PHY managementunit 70 or the MAC/PHY management unit 70 may voluntarily carry out therewriting.

Wireless communication apparatuses configured to support only the normalscheme (in other words, configured not to support the close proximityscheme) do not hold the dot11CloseProximityCommunicationEnabledattribute (need not hold the dot11CloseProximityCommunicationEnabledattribute).

Moreover, the MIB holds attributes specifying the maximum transmissionpower and carrier sense level, respectively, which are used for theclose proximity scheme. The attribute specifying the maximumtransmission power can be named, for example,dot11CloseProximityCommunicationMaximumTransmitPowerLev el. Theattribute specifying the carrier sense level can be named, for example,dot11CloseProximityCommunicationCarrierSenseLevel. According to theabove-described first embodiment, a value fordot11CloseProximityCommunicationMaximumTransmitPowerLev el attribute isset to, for example, 0 dBm. A value fordot11CloseProximityCommunicationCarrierSenseLevel attribute is set to,for example, −48 dBm. Both attribute values may be fixed or may bechanged by the higher layer processing unit 100 or the like.

Alternatively, instead of specifying the maximum transmission power andcarrier sense level themselves, which are used for the close proximityscheme, the present embodiment may provide attributes specifying otherparameters. For example, instead of the maximum transmission power ofthe close proximity scheme, an attribute may be prepared which specifiesthe amount by which the maximum transmission power of the closeproximity scheme is lower than that for the normal scheme (the amountis, for example, 10 dB according to the first embodiment). Instead ofthe carrier sense level for the close proximity scheme, an attribute maybe prepared which specifies the amount by which the carrier sense levelfor the close proximity scheme is greater than the minimum receptionsensitivity level of the PHY scheme (the amount is, for example, 30 dBaccording to the first embodiment).

The PHY processing unit 40 operates in accordance with the closeproximity scheme if the value of dot11CloseProximityCommunicationEnabledattribute is TRUE. That is, the PHY processing unit 40 carries outtransmission so that the transmission power is equal to or lower thanthe value of dot11CloseProximityCommunicationMaximumTransmitPowerLev elattribute. Furthermore, the PHY processing unit 40 determines that CCAis busy or idle based on the value ofdot11CloseProximityCommunicationCarrierSenseLevel attribute.

On the other hand, the PHY processing unit 40 operates in accordancewith the normal scheme if the value ofdot11CloseProximityCommunicationEnabled attribute is FALSE. That is, PHYprocessing unit 40 carries out transmission so that the transmissionpower is equal to or lower than the maximum transmission power of thenormal scheme. Furthermore, the PHY processing unit 40 determines thatCCA is busy or idle based on the minimum reception sensitivity level ofthe PHY scheme. The maximum transmission power of the normal scheme isalso desirably held in the MIB. An attribute specifying the maximumtransmission power of the normal scheme can be named, for example,dot11MaximumTransmitPowerLevel.

The transmission power used by the PHY processing unit 40 may be fixedto the maximum transmission power of the close proximity scheme or thenormal scheme. Alternatively, the MAC processing unit 10 (morespecifically, the transmission processing unit 30) may specify atransmission power equal to or lower than the maximum transmission powerof the close proximity scheme or the normal scheme and notify the PHYprocessing unit 40 of the specified transmission power. Alternatively,the user may specify a transmission power equal to or lower than themaximum transmission power of the close proximity scheme or the normalscheme. In this case, the transmission power specified by the user maybe communicated to the PHY processing unit 40 via the MAC/PHY managementunit 70.

Moreover, the MIB need not necessarily be held in the MAC/PHY managementunit 70. For example, the MIB may be held in a common memory unit (notshown in the drawings). The MIB held in the common memory unit may bedesigned such that the MIB can be referred to (read) by the MAC/PHYmanagement unit 70, the MAC processing unit 10, and the PHY processingunit 40 and that the MAC/PHY management unit 70 can rewrite rewritableattributes.

As described above, in the wireless communication apparatus according tothe second embodiment, the MIB holds various attributes for the closeproximity scheme. Thus, the wireless communication apparatus accordingto the present embodiment can support both a close proximity scheme andnormal scheme and operate appropriately by selecting one of the schemes.

(Third Embodiment)

A wireless communication apparatus according to a third embodimentsupplements the wireless communication apparatuses according to thefirst and second embodiments described above. In the present embodiment,formation and maintenance of a wireless communication group based on theclose proximity scheme (for example, the BSS in IEEE 802.11) will bedescribed. That is, according to the present embodiment, wirelesscommunication apparatuses configured to support the close proximityscheme form a BSS for the close proximity scheme.

In general, in IEEE 802.11, when a BSS is formed, two types of wirelesscommunication apparatuses are present; one type of the wirelesscommunication apparatuses transmits a beacon frame (management frame)(in the present embodiment, the wireless communication apparatusproviding this function is referred to as a first wireless communicationapparatus for convenience), and the other type of wireless communicationapparatus receives the beacon frame (in the present embodiment, thewireless communication apparatus providing this function is referred toas a second wireless communication apparatus for convenience). Thesecond wireless communication apparatus adjusts the operation thereof sothat the operation matches the attribute of the BSS based on theinformation in the received beacon frame. The second wirelesscommunication apparatus further synchronizes the information thereof(for example, a timer value described later) with the synchronizationinformation in the beacon frame. The first wireless communicationapparatus periodically transmits the beacon frame in order to form andmaintain a BSS during a period before formation of the BSS (that is, theperiod when the second wireless communication apparatus joining the BSSis not present) and during a period after the formation of the BSS.

The second wireless communication apparatus may search for the firstwireless communication apparatus based on the received beacon frame(this search is what is called a passive scan). Alternatively, in orderto reduce the search time, the second wireless communication apparatusmay search for the first wireless communication apparatus bytransmitting a management frame to search for the first wirelesscommunication apparatus (for example, a probe request frame in IEEE802.11) and receiving a response frame (for example, a probe responseframe in IEEE 802.11) from the first wireless communication apparatus(this search is what is called an active scan). The probe response framecarries information similar to that in the beacon frame. Hence, thesecond wireless communication apparatus can acquire required informationof the probe response frame instead of from the beacon frame.

The beacon frame is basically transmitted omni-directionally. However,in the millimeter-wave band, an antenna pattern is expected to bequasi-omni-directional depending on the design. In this case, thewireless communication apparatuses need to match the directions of theantenna patterns thereof with each other to some degree. Thus, thesecond wireless communication apparatus configured to carry out anactive scan (configured to transmit a probe request) may initiallytransmit the beacon frame to the first wireless communication apparatus.

Here, a BSS based on the close proximity scheme is a wirelesscommunication group formed by a plurality of wireless communicationapparatuses using the close proximity scheme. Thus, with a fewexceptions, a wireless communication apparatus not supporting the closeproximity scheme cannot join the BSS based on the close proximityscheme.

The wireless communication apparatus according to the present embodimentcarries information indicating that the BSS has an attribute for theclose proximity scheme, in a frame body field of a beacon frame/proberesponse frame transmitted for the BSS based on the close proximityscheme. Thus, upon receiving the beacon frame/probe response frame, thewireless communication apparatus can determine whether or not thesearched-for BSS is based on the close proximity scheme.

In the wireless communication apparatus according to the presentembodiment, the MAC processing unit 10 includes a MAC common processingunit 15 as illustrated in FIG. 4. The MAC common processing unit 15exchanges signals with the MAC/PHY management unit 70. Specifically, theMAC common processing unit 15 receives an instruction from the MAC/PHYmanagement unit 70. Then, the MAC common processing unit 70 converts theinstruction into one suitable for the reception processing unit 20 andthe transmission processing unit 30, and outputs the resultantinstruction. Furthermore, the MAC common processing unit 15 is connectedto the higher layer processing unit 100. Hence, the MAC commonprocessing unit 15 intermediates each of delivery of received data fromthe reception processing unit 20 to the higher layer processing unit 100and delivery of transmitted data from the higher layer processing unit100 to the transmission processing unit 30.

An operation of the wireless communication apparatus according to thepresent embodiment will be described below which is performed when thewireless communication apparatus carries the information indicating thatthe BSS has the attribute for the close proximity scheme in the framebody field of the beacon frame/probe response frame transmitted for theBSS based on the close proximity scheme.

In the wireless communication apparatus according to the presentembodiment, the MIB holds the dot11CloseProximityCommunicationEnabledattribute as in the case of the above-described second embodiment. Whenthe MAC/PHY management unit 70 outputs an instruction (for example, aprimitive called MLME-START.request in IEEE 802.11) to start (formationof) a BSS, a process of transmitting a beacon frame is started. Uponreceiving the instruction, the MAC common processing unit 15 refers tothe value of dot11CloseProximityCommunicationEnabled attribute. If thevalue is TRUE, the MAC common processing unit 15 generates a frame bodywhich carries information indicating that the BSS has the attribute forthe close proximity scheme. The MAC common processing unit 15 thenperiodically provides the transmission processing unit 30 with aninstruction to transmit a beacon frame containing the frame body. Theintervals (Beacon Interval or Beacon Period) at which the beacon frameis transmitted are specified in, for example, the above-describedinstruction to start a BSS. Alternatively, the beacon interval may bespecified in the MIB, and in this case, the MAC common processing unit15 may refer to the MIB. Based on the carrier sense information from thereception processing unit 20, the transmission processing unit 30transmits the beacon frame via the PHY processing unit 40, the frequencyconversion circuit 50, and the antenna 60.

On the other hand, when the wireless communication apparatus accordingto the present embodiment receives a probe request frame from anotherwireless communication apparatus (corresponding to the second wirelesscommunication apparatus), the reception processing unit 20 passes theprobe request frame to the MAC common processing unit 15. If therequirement specified in the frame body of the probe response frame ismet, the MAC common processing unit 15 generates and passes a frame bodyof a probe response frame to the transmission processing unit 30.However, the MAC common processing unit 15 generates the frame body ofthe probe response frame depending on the value ofdot11CloseProximityCommunicationEnabled attribute. Specifically, if thevalue of dot11CloseProximityCommunicationEnabled attribute is TRUE, theMAC common processing unit 15 needs to generate a frame body which holdsinformation indicating that the BSS has the attribute for the closeproximity scheme. Based on carrier sense information from the receptionprocessing unit 20, the transmission processing unit 30 transmits theprobe response frame via the PHY processing unit 40, the frequencyconversion circuit 50, and the antenna 60.

The information indicating that the BSS has the attribute for the closeproximity scheme can be inserted in the frame body field of the beaconframe/probe response frame in a manner exemplified below. A possibledefinition is such that if in the normal scheme, a field indicative ofthe attribute of the BSS is provided and includes a reserved portion,the reserved position can be used to carry the information. For example,the following assumptions are made: the close proximity scheme is usedonly for the millimeter-wave band, the normal scheme on which the closeproximity scheme is based is present in the millimeter-wave band, afield indicative of the attribute of operation in the millimeter-waveband is provided in the frame body field of the beacon frame/proberesponse frame as an information element (IE), and at least 1 bit in thefield indicative of the operation attribute is reserved. In this case, apossible definition is such that the reserved bit can be used torepresent the information indicating whether or not the BSS in operationhas the attribute for the close proximity scheme. That is, the MACcommon processing unit 15 sets the value of the bit to 1 if the BSS inoperation has the attribute for the close proximity scheme, andotherwise (for example, if the BSS in operation has an attribute for thenormal scheme) keeps the value of the bit unchanged (i.e., 0).

The wireless communication apparatus configured to support the closeproximity scheme (and corresponding to the second wireless communicationapparatus) can recognize whether or not the BSS is operated inaccordance with the close proximity scheme by, for example, extractingthe IE, which is indicative of the attribute of operation in themillimeter-wave band, to refer to the value of the bit in which theinformation indicating whether or not the BSS has the attribute for theclose proximity scheme. On the other hand, the wireless communicationapparatus configured not to support the close proximity scheme mayignore the value of the bit which indicates the information whether ornot the BSS has the attribute for the close proximity scheme because thewireless communication apparatus need not recognize the bit.Alternatively, the wireless communication apparatus configured not tosupport the close proximity scheme may recognize that 1 is set in thebit that should be reserved, that is, should be set to 0. The wirelesscommunication apparatus may then determine that a wireless communicationscheme not supported by the wireless communication apparatus is requiredby the BSS, and refrain from joining the BSS.

Now, the operation of the wireless communication apparatus (that is, thewireless communication apparatus supports at least the close proximityscheme) according to the present embodiment when joining a BSS will bedescribed.

Upon determining to search for a BSS, the MAC/PHY management unit 70outputs an instruction to search for a BSS, to the MAC common processingunit 15. The search instruction corresponds to an MLME-SCAN.requestprimitive in IEEE 802.11. The primitive includes parameters illustratedin FIG. 6.

When the Scan Type parameter indicates the passive scan, the MAC commonprocessing unit 15 refers to the Channel List parameter and instructsthe PHY processing unit 40 to shift to a specified frequency channel.Then, the MAC common processing unit 15 collects information of beaconframes among management frames received via the PHY processing unit 40and the reception processing unit 20 during a period equal to or longerthan the Min Channel Time and equal to or shorter than the Max ChannelTime. Here, if the instruction to search for a BSS includes a limitationfor a target condition, the MAC common processing unit 15 collectsinformation only of the beacon frames meeting the target condition. If aplurality of frequency channels are specified in the Channel List, theMAC common processing unit 15 performs the above-described passive scanoperation for each of the specified frequency channels. Once a series ofpassive scan operations ends, the MAC common processing unit 15 passesthe collected information of beacon frames to the MAC/PHY managementunit 70.

On the other hand, when the Scan Type parameter indicates the activescan, the MAC common processing unit 15 generates a frame body of aprobe request frame in accordance with the input instruction. The MACcommon processing unit 15 passes the probe request frame to thetransmission processing unit 30 so that the probe request frame istransmitted in accordance with a BSS search condition (for example, theProbe Delay parameter in FIG. 6) in each of the specified frequencychannels. Unlike in the case of the passive scan, in case of the activescan the MAC common processing unit 15 collects information of proberesponse frames instead of that of beacon frames. As in the case of thepassive scan, if a plurality of frequency channels are specified in theChannel List, the MAC common processing unit 15 performs theabove-described active scan operation for each of the specifiedfrequency channels. Once a series of active scan operations ends, theMAC common processing unit 15 passes the collected information of proberesponse frames to the MAC/PHY management unit 70.

As illustrated in FIG. 6, the BSS search instruction from the MAC/PHYmanagement unit 70 can include the BSS Type parameter to specify thetype of a BSS under scan. If this parameter can specify whether thetarget BSSs are those based on the close proximity scheme, the MACcommon processing unit 15 can utilize the parameter when collectinginformation of beacon frames/probe response frames. That is, when theMAC/PHY management unit 70 provides the MAC common processing unit 15with a search instruction including the BSS Type specifying a BSS basedon the close proximity scheme, the MAC common processing unit 15collects only the beacon frames/probe response frames which carry theinformation indicating that the BSS has the attribute for the closeproximity scheme.

Furthermore, if the MAC/PHY management unit 70 provides the MAC commonprocessing unit 15 with a search instruction including the BSS Typespecifying a BSS based on the close proximity scheme, it is efficientthat the MAC/PHY management unit 70 correspondingly rewrites the valueof the dot11CloseProximityCommunicationEnabled attribute to TRUE. As aresult of the rewrite process, the PHY processing unit 40 uses thecarrier sense level for the close proximity scheme. In other words, theMAC common processing unit 15 collects only the beacon frames/proberesponse frames with a reception level equal to or greater than thecarrier sense level for the close proximity scheme. Thus, the MACprocessing unit 15 can confirm, before joining the BSS, that a signalfrom the BSS corresponding to the collected beacon frames/probe responseframes is received at the carrier sense level for the close proximityscheme or higher. Hence, the rewrite process can avoid a situation inwhich the signal from the target BSS to join fails to meet the carriersense level for the close proximity scheme, resulting in unable torealize the close proximity communication.

The MAC/PHY processing unit 70 determines the BSS which the wirelesscommunication apparatus is to join based on the information of thebeacon frames/probe response frames collected by the MAC commonprocessing unit 15 through the passive scan/active scan. The MAC/PHYmanagement unit 70 provides the MAC common processing unit 15 with aninstruction (for example, the MLME-JOIN.request primitive in IEEE802.11) to join a particular BSS.

Due to a reason such as an application request permits both the normalscheme and the close proximity scheme, the higher layer 100 may providethe MAC/PHY management unit 70 with a BSS search instruction specifyingneither the normal scheme nor the close proximity scheme. Here, thevalue of dot11CloseProximityCommunicationEnabled attribute is FALSE. TheMAC/PHY management unit 70 provides the MAC common processing unit 15with a BSS search instruction not specifying the type of the BSS(whether or not the BSS is based on the close proximity scheme). Even inthis case, the MAC common processing unit 15 can collect information ofthe beacon frames/probe response frames whose BSSs are based on theclose proximity scheme and notify the MAC/PHY management unit 70 of theinformation. However, since the value ofdot11CloseProximityCommunicationEnabled attribute is FALSE as describedabove, the wireless communication apparatus uses the transmission powerand carrier sense level for the normal scheme. That is, more precisely,if a BSS based on the close proximity scheme is present which transmitssignals providing a reception power equal to or greater than the carriersense level for the normal scheme, the MAC common processing unit 15 cancollect information of the beacon frames/probe response frames for theBSS based on the close proximity scheme.

However, to join the BSS based on the close proximity scheme, thewireless communication apparatus needs to rewrite the value ofdot11CloseProximityCommunicationEnabled attribute to TRUE and to use thetransmission power and carrier sense level for the close proximityscheme. Thus, the fact that the wireless communication apparatus canscan the BSS based on the close proximity scheme is not equivalent tothe fact that the wireless communication apparatus can achieve the closeproximity communication after joining the BSS. Specifically, thereception level of the signal from the BSS based on the close proximityscheme may be less than the carrier sense level for the close proximityscheme, which results in inability to realize the close proximitycommunication.

Thus, if the wireless communication apparatus according to the presentembodiment supports both the normal scheme and the close proximityscheme as in the case of the second embodiment, the following operationsare effective. Specifically, the MAC common processing unit 15 adds thereception level of the beacon frames/probe response frames collected bythe scan operation to the information of the frames (information on theBSS). The MAC common processing unit 15 then notifies the MAC/PHYmanagement unit 70 of the resultant information. This notificationcorresponds to an MLME-SCAN.confirm primitive in IEEE 802.11. If suchprimitive is used as a precondition, the above-described operation canbe implemented by adding an item describing the reception level to aparameter called BSSDescription expressing all pieces of BSSinformation. For example, the PHY processing unit 40 passes a MAC frameand the reception level of the MAC frame to the reception processingunit 20. Furthermore, the reception processing unit 20 passes at leastthe information of the beacon frame/probe response frame and thereception level of the frame to the MAC common processing unit 15. TheMAC common processing unit 15 can pass, in addition to the scan result,the reception level of the beacon frame/probe response frame to theMAC/PHY management unit 70 as accompanying information on each BSS. Ifthe scanned BSS has the attribute for the close proximity scheme, theMAC/PHY management unit 70 may determine, based on the reception level,whether or not the wireless communication apparatus can join the BSSbased on the close proximity scheme (whether or not a reception levelequal to or greater than the carrier sense level for the close proximityscheme is obtained if the wireless communication apparatus joins theBSS).

Furthermore, for example, dot11CloseProximityCommunicationImplementedattribute can be defined as an attribute indicating whether or not thewireless communication apparatus supports the close proximity scheme.The attribute is held, for example, in the MIB. That is, if theattribute value is TRUE (indicating that the wireless communicationapparatus supports the close proximity scheme), the MAC commonprocessing unit 15 may pass, in addition to the scan result, thereception level of the beacon frame/probe response frame to the MAC/PHYmanagement unit 70. On the other hand, if the attribute value is FALSE(indicating that the wireless communication apparatus does not supportthe close proximity scheme), the MAC common processing unit 15 maysimply pass the scan result to the MAC/PHY management unit 70 (that is,the MAC common processing unit 15 need not pass the reception level tothe MAC/PHY management unit 70). Moreover, if this attribute fails to bedefined, the MAC common processing unit 15 may determine the wirelesscommunication apparatus not to support the close proximity scheme andbehave in the same manner as that in the case where the attribute valueis FALSE. If dot11CloseProximityCommunicationImplemented attribute isdefined and its value is set to TRUE, then the above-describeddot11CloseProximityCommunicationEnabled attribute is also defined andset to TRUE or FALSE.

For example, the MAC/PHY management unit 70 determines the BSS to bejoined by the wireless communication apparatus based on collected validBSS candidates (that is, BSS candidates determined, based on, forexample, the reception level, to be able to carry out close proximitycommunication if the wireless communication apparatus joins the BSS) aswell as the requirement from the application in the higher layer. If thedetermined BSS has the attribute for the close proximity scheme, theMAC/PHY management unit 70 rewrites the value of thedot11CloseProximityCommunicationEnabled attribute to TRUE to switch thetransmission power and carrier sense level to those used by the closeproximity scheme. The operation of joining the BSS based on the closeproximity scheme is similar to the operation of joining the BSS based onthe normal scheme. That is, the wireless communication apparatusreceives a beacon frame for the BSS based on the close proximity scheme.The wireless communication apparatus then adjusts the operation thereofso that the operation matches the attribute of the BSS based on theinformation in the received beacon frame. The wireless communicationapparatus further synchronizes the information thereof (for example, atimer value described later) with the synchronization information in thebeacon frame.

The information indicating that the BSS has the attribute for the closeproximity scheme may be carried in an association response frame. Theassociation response frame is transmitted to the second wirelesscommunication apparatus by the first wireless communication apparatus ifthe second wireless communication apparatus transmits an associationrequest frame to the first wireless communication apparatus. When theinformation indicating that the BSS has the attribute for the closeproximity scheme is carried in an association response frame, the secondwireless communication apparatus can confirm, during an associationprocess, that the BSS has the attribute for the close proximity scheme.

The above description relates to the operation in which the wirelesscommunication apparatus according to the present embodiment joins theBSS based on the close proximity scheme and the operation in which thewireless communication apparatus according to the present embodimentoperates the BSS based on the close proximity scheme. The followingspecification requirement is expected: for the close proximitycommunication, a wireless communication apparatus using the closeproximity scheme desires to communicate only with wireless communicationapparatuses also using the close proximity scheme. According to thespecification requirement, joining, to the BSS, of a wirelesscommunication apparatus configured not to support the close proximityscheme is preferably excluded or limited. The description below relatesto the operation in which the wireless communication apparatus accordingto the present embodiment operates the BSS based on the close proximityscheme and excludes or limits the joining, to the BSS, of a wirelesscommunication apparatus configured not to support the close proximityscheme.

In IEEE 802.11, the joining to the BSS is defined such that the secondwireless communication apparatus adjusts its operation to match theattribute of the BSS and synchronizes its information with thesynchronization information. Thus, the second wireless communicationapparatus can join the BSS without the need for an authenticationprocedure based on exchange of frames with the first wirelesscommunication apparatus. If the value of the above-describeddot11CloseProximityCommunicationImplemented attribute is TRUE and thesecond wireless communication apparatus desires to join the BSS based onthe normal scheme, then the second wireless communication apparatus mayrecognize that the BSS has the attribute for the close proximity schemebased on the beacon frame and the like and refrain from joining the BSSbased on the close proximity scheme. However, if the value of theattribute is FALSE or the attribute fails to be defined, the secondwireless communication apparatus does not support the close proximityscheme (supports only the normal scheme). Hence, the second wirelesscommunication apparatus may fail to recognize that the BSS has theattribute for the close proximity scheme. That is, the wirelesscommunication apparatus configured not to support the close proximityscheme may join the BSS based on the close proximity scheme by adjustingits operation to match the attribute of the BSS and synchronizing itsinformation with the synchronization information. Consequently, it isdifficult to exclude or limit the joining itself, to the BSS based onthe close proximity scheme, of the wireless communication apparatusconfigured not to support the close proximity scheme. Thus, first, atechnique will be described which excludes or limits the transmission,by the wireless communication apparatus configured not to support theclose proximity scheme, of data frames to the wireless communicationapparatus that is joining the BSS based on the close proximity scheme.

IEEE 802.11 provides an association process. For the BSS based on theclose proximity scheme, a possible specification is such that exchangeof data frames is not allowed to start until the association processcompletes. That is, the wireless communication apparatus that is to jointhe BSS based on the close proximity scheme needs to complete theassociation process before starting exchanging data frames.

The second wireless communication apparatus transmits an associationrequest frame to the first wireless communication apparatus during theassociation process. Information indicating whether or not the secondwireless communication apparatus supports the close proximity scheme iscarried in a frame body field in the association request frame. Forexample, the following assumptions are made: the close proximity schemeis used only in the millimeter-wave band; the normal scheme on which theclose proximity scheme is based is present in the millimeter-wave band;the association request frame based on the normal scheme contains afield indicative of the capability of the wireless communicationapparatus in the millimeter-wave band; and at least 1 bit in this fieldis reserved. In this case, a possible definition is such that thereserved bit is used to represent the information indicating whether ornot the second wireless communication apparatus supports the closeproximity scheme. That is, if the value of thedot11CloseProximityCommunicationImplemented attribute is TRUE, and thevalue of the dot11CloseProximityCommunicationEnabled attribute is FALSE(default), then the MAC common processing unit 15 of the second wirelesscommunication apparatus sets the particular bit to 1 when generating theframe body of the association request frame, in accordance with aninstruction from the MAC/PHY management unit 70. On the other hand, ifthe value of the dot11CloseProximityCommunicationImplemented attributeis FALSE, the MAC common processing unit 15 of the second wirelesscommunication apparatus keeps the particular bit unchanged (i.e., 0).

Then, the first wireless communication apparatus operating the BSS basedon the close proximity scheme receives the association request frame andchecks the value of the particular bit. If the value of the particularbit is 0, the first wireless communication apparatus rejects theassociation. Specifically, the first wireless communication apparatussets Reject in a status code in the association response frame, andtransmits the association response frame to the second wirelesscommunication apparatus. Here, the status code may additionally describethe reason of rejection that the second wireless communication apparatusdoes not support the close proximity scheme. On the other hand, if thevalue of the particular bit is 1, the first wireless communicationapparatus can permit the association depending on other conditions. Topermit the association, the first wireless communication apparatus setsSuccessful in the status code in the association response frame, andtransmits the association response frame to the second wirelesscommunication apparatus. Upon recognizing that the association ispermitted based on the association response frame, the second wirelesscommunication apparatus rewrites the value of thedot11CloseProximityCommunicationEnabled attribute to TRUE, and thenstarts using the close proximity scheme.

In the above description, when the value of thedot11CloseProximityCommunicationImplemented attribute is TRUE, and thevalue of the dot11CloseProximityCommunicationEnabled attribute is FALSE,1 is set in the particular bit in the association request frame.According to the above-described technique, the value of thedot11CloseProximityCommunicationEnabled attribute remains FALSE untilthe association is permitted. That is, the switching, by the wirelesscommunication apparatus, between the use and non-use of the closeproximity scheme depends on a response from another wirelesscommunication apparatus.

Thus, the above-described technique can be modified as follows.Specifically, as described above, the wireless communication apparatusconfigured to support the close proximity scheme (the value of thedot11CloseProximityCommunicationImplemented attribute is TRUE) canrewrite the value of the dot11CloseProximityCommunicationEnabledattribute to TRUE upon determining to join the BSS based on the closeproximity scheme. Setting 1 in the particular bit is also effective ifthe wireless communication apparatus transmits an association requestframe. Specifically, for example, the MAC/PHY management unit 70receives scan results (information on searches for peripheral BSSs) fromthe MAC common processing unit 15 using MLME-SCAN.confirm. The MAC/PHYmanagement unit 70 can select a BSS based on the close proximity schemefrom the scan results and determine to join the BSS. The MAC/PHYmanagement unit 70 instructs the MAC common processing unit 15 to jointhe BSS based on the close proximity scheme using MLME-JOIN.request. TheMAC/PHY management unit 70 then rewrites the value of thedot11CloseProximityCommunicationEnabled attribute to TRUE. Then, theMAC/PHY management unit 70 outputs an MLME-ASSOCIATION.request to theMAC common processing unit 15. In response, the MAC common processingunit 15 generates a frame body of association request frame. At thistime, the MAC common processing unit 15 refers to the value of thedot11CloseProximityCommunicationEnabled attribute. If the value is TRUE,the MAC common processing unit 15 sets 1 in the particular bit in theframe body field of the association request frame. On the other hand, ifthe value of the dot11CloseProximityCommunicationEnabled attribute isFALSE, the MAC common processing unit 15 keeps the particular bit in theframe body of the association request frame unchanged (i.e., 0).According to this technique, the wireless communication apparatus usesthe transmission power and carrier sense level for the close proximityscheme to transmit the association request frame. Thus, the wirelesscommunication apparatus can determine whether or not the frame exchangefor the association is carried out within the communication range forthe close proximity scheme. Specifically, if the wireless communicationapparatus fails to receive an association response frame within apredetermined time after the transmission of the association requestframe, the wireless communication apparatus can determine that thereception level for the association request frame at the communicationpeer (that is, the above-described first wireless communicationapparatus) is less than the carrier sense level for the close proximityscheme. That is, the wireless communication apparatus can determine thatthe distance from the communication peer exceeds the communication rangefor the close proximity scheme. The MAC/PHY management unit 70 canspecify the duration for which the wireless communication apparatuswaits for an association response frame. Furthermore, in providing theMAC common processing unit 15 with an MLME-ASSOCIATION.request, theMAC/PHY management unit 70 can notify the MAC common processing unit 15of the duration specified in the primitive in theMLME-ASSOCIATION.request.

Now, a technique will be described which excludes or limits thetransmission of data frames by the wireless communication apparatusconfigured not to support the close proximity scheme after joining a BSSbased on the close proximity scheme.

For example, the first wireless communication apparatus can create aschedule in which wireless communication apparatuses for which theassociation is not permitted are prevented from transmitting data framesduring the beacon interval. If the normal scheme on which the closeproximity scheme is based involves a mechanism in which the wirelesscommunication apparatuses joining a BSS transmit frames in accordancewith the transmission schedule for the beacon interval, the mechanismcan also be utilized for the close proximity scheme. Specifically, asillustrated in FIG. 5, the first wireless communication apparatus maycreate a schedule in which management frames such as the associationrequest frame can be transmitted only during a given period of thebeacon interval and that only the first wireless communication apparatusor the wireless communication apparatuses for which the first wirelesscommunication apparatus permits the association can transmit data framesduring all of the remaining period of the beacon interval. The scheduleinformation is provided to each wireless communication apparatus via thebeacon frame.

In FIG. 5, the first wireless communication apparatus is denoted by“STA1”, and one wireless communication apparatus for which the firstwireless communication apparatus permits the association is denoted by“STA2”. That is, in the example illustrated in FIG. 5, no period isscheduled for the wireless communication apparatuses other than STA1 andSTA2 to transmit data frames. In FIG. 5, during a management frametransmission enabled period, management frames such as the associationrequest frame are transmitted. However, the first wireless communicationapparatus can also designate certain wireless communication apparatusespermitted to transmit data frames during the management frametransmission enabled period.

The wireless communication apparatus configured not to support the closeproximity scheme may not be able to recognize that the BSS joined by thewireless communication apparatus has the attribute for the closeproximity scheme. However, no period is scheduled for the wirelesscommunication apparatus to transmit data frames, and thus the wirelesscommunication apparatus can not transmit any data frames. Thus, thewireless communication apparatus configured not to support the closeproximity scheme may desire to have its transmission period scheduledand generate and transmit an association request frame to the firstwireless communication apparatus during the management frametransmission enabled period. However, the wireless communicationapparatus configured not to support the close proximity scheme cannotset the particular bit, which is prepared in the association requestframe to indicate whether or not the close proximity scheme issupported, to 1. Thus, the first wireless communication apparatus canreject the association with the wireless communication apparatusconfigured not to support the close proximity scheme. Even if a certainmanagement frame is defined to request scheduling of a transmissionperiod, similar effects can be exerted by defining the particular bit asin the case with the association request frame (that is, a schedulerequest from the wireless communication apparatus configured not tosupport the close proximity scheme may be rejected or the transmissionperiod for the wireless communication apparatus may be excluded from theschedule).

Furthermore, it is also effective to limit the transmission period ofthe wireless communication apparatus whose association is not permitted(that is, the wireless communication apparatus configured not to supportthe close proximity scheme) within the beacon interval. Specifically,the management frame transmission enabled period in the exampleillustrated in FIG. 5 may be replaced with a contention period. Duringthe contention period, transmissible frames are not limited to themanagement frames, and the wireless communication apparatus which cantransmit frames is also not limited. According to this schedule, thewireless communication apparatus configured not to support the closeproximity scheme can transmit data frames only during the contentionperiod. It is desirable to set the contention period short enough tosatisfy a transmission request (QoS (Quality of Service) request) fromthe wireless communication apparatus utilizing the close proximityscheme. When the contention period is set to be sufficiently short, evenif the wireless communication apparatus configured not to support theclose proximity scheme joins a BSS based on the close proximity scheme,frame transmission from such wireless communication apparatus issubstantially prevented from obstructing frame transmission from thewireless communication apparatus utilizing the close proximity scheme.

Additionally, if a parameter essential for joining the BSS in connectionwith the attribute of the BSS can be defined, this mechanism is alsoeffectively utilized. Specifically, in connection with such a parameter,the above-described first wireless communication apparatus inserts acode that can be understood by the wireless communication apparatusconfigured to support the close proximity scheme and which cannot beunderstood by the wireless communication apparatus configured not tosupport the close proximity scheme. Insertion of the code allows thewireless communication apparatus configured not to support the closeproximity scheme to be excluded from the BSS based on the closeproximity scheme. For example, it is assumed that an IE indicative of anMCS set used for the BSS is present and that a method is available whichindicates, in the IE, an MCS essential for reception in the BSS. Thefirst wireless communication apparatus utilizes this method to define acode that is not actually indicating an MCS, but for the close proximityscheme. The wireless communication apparatus configured to support theclose proximity scheme understands that the code is defined for theclose proximity scheme and can join the BSS. On the other hand, thewireless communication apparatus configured not to support the closeproximity scheme cannot understand the code. Furthermore, the MCSindicated by the code is defined to be essential for reception in theBSS. Therefore, the wireless communication apparatus cannot join the BSS(cannot give an instruction to join the BSS).

In addition, for the normal scheme on which the close proximity schemeis based, if a frame is defined to expel certain wireless communicationapparatuses from the BSS, the frame can be effectively utilized.Specifically, upon recognizing that the wireless communication apparatusconfigured not to support the close proximity scheme is joining the BSSbased on the close proximity scheme, the first wireless communicationapparatus may transmit the frame to expel the wireless communicationapparatus from the BSS. However, the first wireless communicationapparatus may fail to recognize that the wireless communicationapparatus configured not to support the close proximity scheme isjoining the BSS based on the close proximity scheme until the wirelesscommunication apparatus starts exchanging data frames.

As described above, according to the wireless communication apparatus ofthe third embodiment, the wireless communication apparatuses supportingthe close proximity scheme can form a BSS based on the close proximityscheme. In the description of the present embodiment and otherembodiments, specific management frames such as the beacon frame and theprobe response frame are exemplified. However, these frames may bereplaced with other management frames.

(Fourth Embodiment)

A wireless communication apparatus according to a fourth embodimentsupplements the above-described wireless communication apparatusesaccording to the first to third embodiments. Specifically, the wirelesscommunication apparatus according to the present embodiment enablesconnections based on the close proximity scheme without depending onnetwork identifiers provided in the normal scheme.

For example, IEEE 802.11 specifies an SSID (Service Set IDentifier),which is an identifier of a network including the BSS, as a piece ofinformation indicative of the attribute of the BSS. A use case ispossible in which in connection with the close proximity scheme,communication starts immediately when wireless communication apparatusescome close to each other. With this use case taken into account, even ifthe normal scheme requires an SSID, the close proximity scheme mayrequire not to limit the communication peer nor to ask the networkidentifier.

Thus, if the close proximity scheme needs to follow the policy of thenormal scheme and to specify a certain SSID, the wireless communicationapparatus according to the present embodiment may for example, use arandom number counter or utilize an identifier specific to the wirelesscommunication apparatus having started a BSS based on the closeproximity scheme to temporarily determine an SSID. Then, the wirelesscommunication apparatuses joining the BSS based on the close proximityscheme may ignore the SSID.

As described above, the wireless communication apparatus according tothe fourth embodiment ignores the network identifier in the BSS based onthe close proximity scheme. Thus, the wireless communication apparatusaccording to the present embodiment can realize close proximitycommunication which is suitable for the use case expected for the closeproximity scheme.

(Fifth Embodiment)

A wireless communication apparatus according to a fifth embodimentsupplements the above-described wireless communication apparatusesaccording to the first to fourth embodiments. The wireless communicationapparatus according to the present embodiment reduces the time requiredbefore starting exchange of data frames in the close proximity schemecompared to that in the normal scheme.

Here, some use cases of the close proximity communication require areduction in the time required before starting the data communication(that is, exchange of data frames). In other words, the time required toset up a communication link is desired to be reduced.

The time required to set up a communication link includes many elements;for example, the time required to select a channel on which a BSS basedon the close proximity scheme operates, the time required to search fora BSS based on the close proximity scheme, and the time for negotiationrequired if wireless communication apparatuses configured toperiodically transmit beacon frames contend with each other. Some usecases of the close proximity communication may relate to only some ofthese elements.

First, a reduction in the time required to select a channel on which aBSS based on the close proximity scheme operates will be described.According to the above-described first embodiment, since the closeproximity scheme uses a higher carrier sense level than the normalscheme (the carrier sense level of the normal scheme is the minimumreception sensitivity level of the physical scheme), the probability ofdetecting interference in the close proximity scheme is lower than thatin the normal scheme. Hence, in selection of the channel on which theBSS based on the close proximity scheme operates, the number ofcandidate channels (channels with less interference) for the closeproximity scheme is likely to be greater than that for the normalscheme, in other words, it is likely to be easier to find a clearchannel. Thus, the wireless communication apparatus according to thepresent embodiment uses a carrier sense level similar to that in thefirst embodiment to enable a reduction in the time required to selectthe channel on which the BSS based on the close proximity schemeoperates.

Now, a reduction in the time required to search for a BSS based on theclose proximity scheme will be described. The time required for thesearch depends on the maximum beacon interval likely to be used for theBSS. Thus, the wireless communication apparatus according to the presentembodiment limits the maximum beacon interval for the close proximityscheme so that the maximum beacon interval for the close proximityscheme is shorter than that for the normal scheme. For example, thewireless communication apparatus sets the maximum beacon interval forthe normal scheme to 1 s, while setting the maximum beacon interval forthe close proximity scheme to 10 ms. With this setting, when thewireless communication apparatus searches for a BSS based on the closeproximity scheme on a particular frequency channel by means of a passivescan, the search may continue for 10 ms. On the other hand, when thewireless communication apparatus searches for a BSS based on the normalscheme on a particular frequency channel by means of a passive scan, thesearch needs to continue for 1 s. Consequently, the time required forthe passive scan in the close proximity scheme may be shorter than thatin the normal scheme.

On the other hand, for the active scan, a procedure may be carried outin which wireless communication apparatuses using the millimeter-waveband to transmit the beacon frame to each other to adjust thedirectivity angle of the antenna. In the procedure, if the beaconinterval is randomly selected from the range equal to or smaller thanthe maximum beacon interval, the maximum beacon interval for the closeproximity scheme can be effectively limited so as to be shorter thanthat for the normal scheme. That is, the time required for the activescan may be set to be shorter for the close proximity scheme than forthe normal scheme.

Now, a reduction in the time required for negotiation required whenwireless communication apparatuses periodically transmitting beaconframes contend with each other will be described. For example, it isassumed that each of the two wireless communication apparatuses hasstarted an application using the close proximity scheme and is forming aBSS based on the close proximity scheme. One of the wirelesscommunication apparatuses (in the present embodiment, referred to as thefirst wireless communication apparatus for convenience) starts toperiodically transmit the beacon frame earlier than the other wirelesscommunication apparatus (in the present embodiment, referred to as thesecond wireless communication apparatus for convenience). However, thesecond wireless communication apparatus desires to be a wirelesscommunication apparatus that periodically transmits the beacon frame inaccordance with the requirements of the application or the like (forexample, the wireless communication apparatus desires to set the beaconinterval to a desired value or to manage the scheduling of the beaconinterval) (this wireless communication apparatus is also referred to asa group owner).

In this situation, the second wireless communication apparatus generallytransmits a request to acquire the right to transmit the beacon frame (arequest to become the group owner), to the first wireless communicationapparatus. Then, the first and second wireless communication apparatusesnegotiate over which of the wireless communication apparatuses is toacquire the right to transmit the beacon frame (which is to become thegroup owner). The negotiation is conventionally carried out byexchanging management frames between the wireless communicationapparatuses. Specifically, two frames initially exchanged between thewireless communication apparatuses each indicate the requirement levelof the transmitting wireless communication apparatus. Then, the wirelesscommunication apparatus with the higher requirement level acquires theright to transmit the beacon frame (becomes the group owner). Thus, thenegotiation requires a total of three frames, the two frames indicatingthe requirement levels of the respective wireless communicationapparatuses and one frame indicating the final decision (indicatingwhether the transmission right is handed over or not). Furthermore, insuch negotiation, it is difficult to make unique determination of whichof the wireless communication apparatuses is to acquire the right totransmit the beacon frame when the requirement level is the same.Moreover, each of the wireless communication apparatuses cannotrecognize the requirement level of the other until starting the frameexchange for the negotiation.

Thus, if the requirement level of the wireless communication apparatusaccording to the present embodiment is the same as that of thecommunication peer, the wireless communication apparatus refers toidentifiers (for example, MAC addresses) specific to the two wirelesscommunication apparatuses. Specifically, the wireless communicationapparatus compares its identifier with that of the communication peer todetermine that one of the wireless communication apparatuses having thelarger identifier value (or the smaller identifier value) is to acquirethe right to transmit the beacon frame.

Moreover, the first wireless communication apparatus may effectivelydescribe the requirement level thereof in the frame body field of thebeacon frame. According to this technique, upon receiving the beaconframe from the first wireless communication apparatus, the secondwireless communication apparatus can recognize the requirement level ofthe first wireless communication apparatus. Thus, the second wirelesscommunication apparatus may compare the requirement level thereof withthat of the first wireless communication apparatus. Then, the secondwireless communication apparatus may transmit a frame for a request tostart negotiation to the first wireless communication apparatus if therequirement level of the second wireless communication apparatus ishigher than that of the first wireless communication apparatus. Thesecond wireless communication apparatus may concede the right totransmit the beacon frame if the requirement level of the first wirelesscommunication apparatus is higher than that of the second wirelesscommunication apparatus.

In general, the MAC address of the transmitting wireless communicationapparatus (in the present example, the first wireless communicationapparatus) is described in the beacon frame as the identifier (BSSID) ofthe wireless communication group. Hence, like the requirement level, theMAC address of the first wireless communication apparatus can bereferred to through the received beacon frame. If the requirement levelof the second wireless communication apparatus is the same as that ofthe first wireless communication apparatus, the second wirelesscommunication apparatus compares the MAC address thereof with that ofthe first wireless communication apparatus. Then, the second wirelesscommunication apparatus may transmit a frame for a request to startnegotiation to the first wireless communication apparatus if the MACaddress of the second wireless communication apparatus is greater thanthat of the first wireless communication apparatus. The second wirelesscommunication apparatus may concede the right to transmit the beaconframe if the MAC address of the first wireless communication apparatusis greater than that of the second wireless communication apparatus.

Thus, when the requirement level of the first wireless communicationapparatus is described in the frame body field of the beacon frame, thesecond wireless communication apparatus can recognize the requirementlevel of the first wireless communication apparatus before startingnegotiation. This allows frame exchanges useless for negotiation to beomitted. In other words, the second wireless communication apparatus canpre-recognize whether or not the second wireless communication apparatuscan acquire the right to transmit the beacon frame. Thus, if the secondwireless communication apparatus cannot acquire the right to transmitthe beacon frame, the second wireless communication apparatus avoidstransmitting the request frame to the first wireless communicationapparatus. On the other hand, if the second wireless communicationapparatus can acquire the right to transmit the beacon frame, the secondwireless communication apparatus transmits the request frame to thefirst wireless communication apparatus. However, the first wirelesscommunication apparatus returns a response frame indicating that thefirst wireless communication apparatus accepts the request, thus thenegotiation is finished via a total of two frames. That is, the timerequired for the negotiation in the close proximity scheme is shorterthan that in the normal scheme.

Similar effects are exerted by describing the requirement level in theframe body field of the probe response frame instead of the beaconframe.

When the requirement levels of both wireless communication apparatusesare the same, a parameter other than the identifier specific to eachwireless communication apparatus (here, which was the MAC address) maybe used for comparison. For example, the wireless communicationapparatus may use a timer value for comparison. Specifically, the beaconframe is used to synchronize another wireless communication apparatus,and the timer value held by the transmission source is described in thebeacon frame. In IEEE 802.11, the timer value held by the transmissionsource is described in a Timestamp field. In general, when the wirelesscommunication apparatus determines to join a BSS (that is, the MAC/PHYmanagement unit 70 outputs an MLME-JOIN.request to the MAC commonprocessing unit 15), the reception processing unit 20 receives thebeacon frame from the BSS which the wireless communication apparatus isto join. The MAC common processing unit 15 matches the timer value ofthe wireless communication apparatus with the Timestamp value in thereceived beacon frame (synchronizes the timer value with the Timestampvalue).

The operation involved in the comparison of the timer value will bedescribed. It is assumed that when the MAC/PHY management unit 70determines the BSS which the wireless communication apparatus is tojoin, the wireless communication apparatus may desire to acquire theright to transmit the beacon frame for the BSS (to become the groupowner). Then, the requirement levels of the wireless communicationapparatuses are compared with each other as described above. If therequirement level described in the received beacon frame is lower thanthe requirement level of the wireless communication apparatus, theMAC/PHY management unit 70 instructs the MAC common processing unit 15to transmit the frame for a request to start negotiation. If therequirement level of the wireless communication apparatus is lower thanthe requirement level described in the received beacon frame, theMAC/PHY management unit 70 outputs the MLME-JOIN.request to the MACcommon processing unit 15 in accordance with the normal procedurewithout instructing the MAC common processing unit 15 to transmit theframe for a request to start negotiation. Furthermore, if therequirement level of the wireless communication apparatus is the same asthe requirement level described in the received beacon frame, theMAC/PHY management unit 70 also instructs the MAC common processing unit15 to transmit the frame for a request to start negotiation. However,the MAC common processing unit 15 carries out comparison of the timervalue before transmitting the request frame. Specifically, the MACcommon processing unit 15 compares the timer value of the wirelesscommunication apparatus with the Timestamp value in the received beaconframe. If the timer value of the wireless communication apparatus isgreater than the TimeStamp value, the MAC common processing unit 15transmits the request frame in accordance with the instruction. On theother hand, if the Timestamp value in the received beacon frame isgreater than the timer value of the wireless communication apparatus,the MAC common processing unit 15 may synchronize the timer value of thewireless communication apparatus with the Timestamp value. The MACcommon processing unit 15 may then notify the MAC/PHY management unit 70of the synchronization (that is, the requirement level of the wirelesscommunication apparatus is the same as that of the communication peer,but the timer value of the wireless communication apparatus is smallerthan that of the communication peer). The timer values of the wirelesscommunication apparatus and the communication peer are rarely the same.In this case, the MAC common processing unit 15 may randomly determinewhether or not to acquire the right to transmit the beacon frame, forexample, on the cast of a dice with only 1 or 0 on each side thereof. Inany case, if the request frame is transmitted, the negotiation isfinished via a total of two frames as in the case of the above-describedexample.

In the close proximity scheme, the above-described technique allowsomission of frame exchange useless for the negotiation for the right totransmit the beacon frame and enables a reduction in the number offrames exchanged during the negotiation. Thus, the time required for thenegotiation can be reduced.

Furthermore, as described above, for exchange of management frames, thetime for which the wireless communication apparatus waits to receive anext management frame after transmitting one management frame can beeffectively set to be shorter for the close proximity scheme than forthe normal scheme. This control enables a reduction in the time requireduntil the frame exchange completes. For example, as described in thethird embodiment, the MAC/PHY management unit 70 can specify the timefor which the wireless communication apparatus waits for an associationresponse and notifies the MAC common processing unit 15 of the specifiedtime through the MLME-ASSOCIATION.request primitive. Then, if the closeproximity scheme is selected (dot11CloseProximityCommunicationEnabledattribute is set to TRUE), the MAC/PHY management unit 70 may specify ashorter time for the close proximity scheme than for the normal scheme.For exchange of other management frames, a similar technique can be usedto exert similar effects. That is, in the close proximity scheme, theMAC/PHY management unit 70 can specify a shorter time to wait for themanagement frame than for the normal scheme and notify the MAC commonprocessing unit 15 of the specified time through theMLME-ASSOCIATION.request primitive.

As described above, the wireless communication apparatus according tothe present embodiment sets the time required before starting theexchange of data frames to be shorter for the close proximity schemethan for the normal scheme. Thus, the wireless communication apparatusaccording to the present embodiment allows a reduction in the timerequired to set up a communication link. This serves to provide closeproximity communication suitable for use cases expected for the closeproximity scheme.

(Sixth Embodiment)

A wireless communication apparatus according to a sixth embodiment isobtained by partly changing the wireless communication apparatusesaccording to the above-described first to fifth embodiments.Specifically, the wireless communication apparatus according to thepresent embodiment sets the transmission power and antenna gain used inaccordance with the normal scheme to be similar to those used inaccordance with the close proximity scheme.

In the wireless communication apparatus according to the presentembodiment, the value of the above-describeddot11CloseProximityCommunicationImplemented attribute is assumed to beTRUE. For example, the wireless communication apparatus sets the maximumtransmission power of the normal scheme to 10 dBm as in the case of theabove-described example but sets the default value to 0 dB, which is thesame as the maximum transmission power of the close proximity scheme.

Moreover, the wireless communication apparatus basically avoids changingthe antenna gain for the normal scheme unless the following antennagains for the close proximity scheme are changed: the antenna gain useduntil a connection link is established and the antenna gain used toexchange data frames.

As described above, the wireless communication apparatus according tothe sixth embodiment basically limits the difference between theoperation in the normal scheme and the operation in the close proximityscheme to the carrier sense level. Thus, the wireless communicationapparatus according to the present embodiment reduces a processing loadinvolved in changing the communication scheme compared to that of thewireless communication apparatuses according to the other embodiments.Furthermore, default behavior in the normal scheme is similar to that inthe close proximity scheme, leading to the similarity in receptionconditions between the normal scheme and the close proximity scheme. Asa result, finding a communication peer meeting the reception conditionsfor the close proximity scheme becomes easy. This in turn increases thenumber of opportunities exploited by the wireless communicationapparatus to select the close proximity scheme and thus the number ofopportunities exploited by the wireless communication apparatus toutilize a close proximity application.

(Seventh Embodiment)

A wireless communication apparatus according to the present embodimentsupplements the wireless communication apparatuses according to theabove-described first to sixth embodiments. Specifically, the wirelesscommunication apparatus according to the present embodiment setscontention parameters for the close proximity scheme to more appropriatevalues.

IEEE 802.11 is a wireless communication scheme based on the carriersense as described above, and more specifically adopts CSMA/CA (CarrierSense Multiple Access with Collision Avoidance). CSMA/CA will bedescribed below in brief. For example, with a simple mechanism in whichfor example, the wireless communication apparatus carries out thecarrier sense to transmit a signal upon determining that the medium isidle, if a plurality of wireless communication apparatuses are waitingfor the medium to be free, signals may be transmitted at the same timeand contend with each other. Thus, according to CSMA/CA, each wirelesscommunication apparatus randomly selects one of the values within apredetermined range (the values are referred to as a contention window)and waits in accordance with the selected value before transmitting asignal.

According to the normal scheme, for data frames, when data is passedfrom the higher layer, the priority (in IEEE 802.11, the User Priority(simply referred to as UP)) of the data is indicated. Furthermore, basedon the priority of the data, priorities for access to the medium (inIEEE 802.11, the priorities are referred to as Access Categories (simplyreferred to as ACs)) are assigned to the data frames. Then, the dataframes are transmitted in accordance with contention parametersspecified for the respective priorities to access the medium. Thecontention parameter includes, for example, the minimum and maximumvalues of the contention window (in IEEE 802.11, referred to as CWminand CWmax, respectively), the frame interval time (in IEEE 802.11,referred to as AIFSN which is expressed in units called slots) for whichthe wireless communication apparatus waits before starting countdown ofthe selected random number, and the maximum transmission rightacquisition time (in IEEE 802.11, referred to as TXOP limit).

In general, the close proximity scheme involves a smaller number ofwireless communication apparatuses that contend with one another thanthe normal scheme. It is thus assumed that realizing point-to-pointcommunication is often sufficient for the close proximity scheme. Hence,the close proximity scheme can sufficiently avoid contentions even ifthe contention window for the close proximity scheme is narrower thanthat for the normal scheme. Rather, setting a contention window for theclose proximity scheme that is equivalent in width to that for thenormal scheme results in a high probability that the wirelesscommunication apparatus has to wait for an improperly long time.Furthermore, transmission of signals is delayed depending on the waittime, increasing the time for which the medium is uselessly andinefficiently idle. Thus, the wireless communication apparatus accordingto the present embodiment sets the width of the contention window to besmaller for the close proximity scheme than that for the normal scheme.For example, the wireless communication apparatus sets the value ofCWmax for each AC to be smaller than that for the normal scheme. Ofcourse, the wireless communication apparatus may set other parametersappropriate for the close proximity scheme. Alternatively, while aparameter set is provided for each AC in the normal scheme, the wirelesscommunication apparatus may exclusively use one parameter set (in IEEE802.11, specified for AC_VO) including the smallest CWmax for the closeproximity scheme.

If the values of the contention parameters are redefined for the closeproximity scheme separately from those for the normal scheme, thecontention parameter set for the close proximity scheme may be held inthe MIB as, for example, dot11CPCATable attribute following the otherprevious embodiments. Similarly, if other parameters used for the normalscheme are desirably redefined for the close proximity scheme, all theredefined parameters may be held in the MIB as a close proximityparameter set (for example, dot11CloseProximityParameterTableattribute).

As described above, the wireless communication apparatus according tothe seventh embodiment redefines the contention parameters for the closeproximity scheme. Thus, the wireless communication apparatus accordingto the seventh embodiment can implement efficient CSMA/CA in the closeproximity scheme.

(Eighth Embodiment)

A wireless communication apparatus according to an eighth embodimentsupplements the wireless communication apparatuses according to theabove-described first to seventh embodiments. Specifically, in thepresent embodiment, operations which are performed when the wirelesscommunication apparatuses connected together in accordance with theclose proximity scheme move away from each other so that the distancebetween the wireless communication apparatuses exceeds the communicationrange will be described.

In general, the normal scheme is designed under the policy that theconnection is attempted to be maintained even if the status of receptionof signals from the communication peer is degraded or signals from thecommunication peer cannot be received. On the other hand, the closeproximity scheme may be required to start communication when thewireless communication apparatuses come close to each other so that thedistance between the wireless communication apparatuses is within thecommunication range and automatically break the connection between thewireless communication apparatuses when the wireless communicationapparatuses move away from each other so that the distance between thewireless communication apparatus exceeds the communication range.

Thus, when the wireless communication apparatus according to the presentembodiment operating under the close proximity scheme fails to receive aframe for a given period from the communication peer with which exchangeof data frames has been started, the wireless communication apparatusdetermines that the communication peer has moved away from the wirelesscommunication apparatus. The wireless communication apparatus thendeletes information on the status of the connection with thecommunication peer. The given period is specified, for example, in theMIB. For example, the MAC common processing unit 15 monitors the statusof reception of frames from the communication peer while referring tothe given period. The MAC common processing unit 15 holds a managementtable configured to manage information on other wireless communicationapparatuses whose associations are permitted. Upon determining that thewireless communication apparatus corresponding to the communication peerhas moved away, the MAC common processing unit 15 deletes theinformation on the status of connection with the wireless communicationapparatus from the management table. Additionally, if the transmissionperiod for the wireless communication apparatus is scheduled during thebeacon interval, the MAC common processing unit 15 also cancels thescheduled transmission period.

When the wireless communication apparatus according to the eighthembodiment operating under the close proximity scheme fails to receive aframe for the given period from the communication peer with whichexchange of data frames has been started, the wireless communicationapparatus determines that the communication peer has moved away from thewireless communication apparatus. The wireless communication apparatusthen deletes information on the status of the connection with thecommunication peer. Thus, the wireless communication apparatus accordingto the present embodiment operating under the close proximity scheme canautomatically break the connection between the two wirelesscommunication apparatuses when the wireless communication apparatuscorresponding to the communication peer gets away from the wirelesscommunication apparatus according to the present embodiment so that thedistance between the two wireless communication apparatuses exceeds thecommunication range.

The wireless communication apparatus according to the present embodimentuses a higher carrier sense level for the close proximity scheme thanthat for the normal scheme as is the case with the above-described firstembodiment, to limit receivable MAC frames to those transmitted withinthe communication range for the close proximity scheme. Thus, if thewireless communication apparatus corresponding to the communication peerhas moved away so that the distance between the two wirelesscommunication apparatuses exceeds the communication range, the MACframes transmitted by the wireless communication apparatus correspondingto the communication peer fail to be passed to the MAC processing unit10. As a result, no frame is received for a certain period.

(Ninth Embodiment)

A ninth embodiment comprises a buffer in addition to the components ofthe wireless communication apparatus in FIG. 1, FIG. 3, or FIG. 4. Theinclusion of the buffer in the wireless communication apparatus enablestransmitted and received frames to be held in the buffer. As a result, aretransmission process or an external output process can be easilycarried out.

(Tenth Embodiment)

A tenth embodiment comprises a bus, a processor unit, and an externalinterface unit, in addition to the components of the wirelesscommunication apparatus according to the ninth embodiment. The processorunit and the external interface unit are connected to the buffer via abus. Firmware operates in the processor unit. Thus, the firmwareincluded in the wireless communication apparatus enables the functionsof the wireless communication apparatus to be easily changed byrewriting the firmware.

(Eleventh Embodiment)

An eleventh embodiment comprises a clock generation unit in addition tothe components of the wireless communication apparatus in FIG. 1, FIG.3, or FIG. 4. The clock generation unit generates and outputs a clock tothe outside of the wireless communication apparatus through an outputterminal. Thus, the clock generated inside the wireless communicationapparatus is output to the outside so that the output clock is used tooperate a host side. This enables the host side and the wirelesscommunication apparatus to operate synchronously.

(Twelfth Embodiment)

A twelfth embodiment includes a power supply unit, a power supplycontrol unit, and a wireless power feeding unit in addition to thecomponents of the wireless communication apparatus in FIG. 1, FIG. 3, orFIG. 4. The power supply control unit is connected to the power supplyunit and the wireless power feeding unit to control selection of a powersupply to be provided to the wireless communication apparatus. Thus, thepower supply provided in the wireless communication apparatus can becontrolled so as to enable operations with reduced power consumption.

(Thirteenth Embodiment)

A thirteenth embodiment includes a SIM card in addition to thecomponents of the wireless communication apparatus according to thetwelfth embodiment. The SIM card is connected to the MAC processing unit10 or the MAC/PHY management unit 70. Thus, the SIM card provided in thewireless communication apparatus enables an authentication process to beeasily carried out.

(Fourteenth Embodiment)

A fourteenth embodiment includes a motion picturecompression/decompression unit in addition to the components of thewireless communication apparatus according to the tenth embodiment. Themotion picture compression/decompression unit is connected to the bus.Thus, the motion picture compression/decompression unit provided in thewireless communication apparatus enables transmission of compressedmotion pictures and decompression of received compressed motion picturesto be easily achieved.

(Fifteenth Embodiment)

A fifteenth embodiment includes an LED unit in addition to thecomponents of the wireless communication apparatus in FIG. 1, FIG. 3, orFIG. 4. The LED unit is connected to the MAC processing unit 10 or thePHY processing unit 40. Thus, the LED unit provided in the wirelesscommunication apparatus enables the user to be easily notified of theoperational status of the wireless communication apparatus.

(Sixteenth Embodiment)

A sixteenth embodiment includes a vibrator unit in addition to thecomponents of the wireless communication apparatus in FIG. 1, FIG. 3, orFIG. 4. The vibrator unit is connected to the MAC processing unit 10 orthe PHY processing unit 40. Thus, the vibrator unit provided in thewireless communication apparatus enables the user to be easily notifiedof the operational status of the wireless communication apparatus.

(Seventeenth Embodiment)

A seventeenth embodiment comprises, in addition to the components of thewireless communication apparatus in FIG. 1, FIG. 3, or FIG. 4, theplurality of different PHY processing units 40 as described in the firstembodiment, and further includes a wireless switching unit. The wirelessswitching unit is connected to the plurality of different PHY processingunits 40 to switch communications based on the different PHY processingunits 40. Thus, the plurality of PHY processing units 40 provided in thewireless communication apparatus enable switching to the communicationusing the appropriate PHY processing unit 40 depending on the situation.

(Eighteenth Embodiment)

An eighteenth embodiment comprises, in addition to the components of thewireless communication apparatus in FIG. 1, FIG. 3, or FIG. 4, theplurality of different PHY processing units 40 as described in the firstembodiment, and pairs each of the reception processing unit 20 and thetransmission processing unit 30 which pairs correspond to the respectivePHY processing units 40. The eighteenth embodiment further includes awireless switching unit. The wireless switching unit is connected so asto allow switching among the pairs of the reception processing unit 20and the transmission processing unit 30. The wireless switching unitswitches among a plurality of communication schemes based on thedifferent reception processing units 20, transmission processing units30, and PHY processing units 40. Thus, the plurality of different setsof each of the reception processing unit 20, transmission processingunit 30, and PHY processing unit 40 provided in the wirelesscommunication apparatus enable switching to the communication using theappropriate set of the reception processing unit 20, transmissionprocessing unit 30, and PHY processing unit 40.

(Nineteenth Embodiment)

A nineteenth embodiment includes a switch (SW) in addition to thecomponents of the wireless communication apparatus according to theseventeenth embodiment. The switch is connected to the antenna 60, theplurality of different PHY processing units 40, and the wirelessswitching unit. Thus, the switch provided in the wireless communicationapparatus enables switching to communication using the appropriate PHYprocessing unit 40 depending on the situation, with the antenna sharedby the PHY processing units 40.

(Twentieth Embodiment)

A twentieth embodiment includes a switch (SW) in addition to thecomponents of the wireless communication apparatus according to theeighteenth embodiment. The switch is connected to the antenna 60, theroot of the pair of the reception processing unit 20 and thetransmission processing unit 30, and the wireless switching unit. Thus,the switch provided in the wireless communication apparatus enablesswitching to communication using the appropriate set of the receptionprocessing unit 20, transmission processing unit 30, and PHY processingunit 40 depending on the situation, with the antenna shared by the sets.

The processing in each of the above-described embodiments can beimplemented using a general-purpose computer as basic hardware. Aprogram implementing the processing in each of the above-describedembodiments may be stored in a computer-readable storage medium forprovision. The program is stored in the storage medium as a file in aninstallable or executable format. The storage medium may be a magneticdisk, an optical disc (CD-ROM, CD-R, DVD, or the like), a magnetoopticdisc (MO or the like), a semiconductor memory, or the like. That is, thestorage medium may be in any format provided that the program can bestored in the storage medium and read by the computer. Furthermore, theprogram implementing the processing in each of the above-describedembodiments may be stored in a computer (server) connected to a networksuch as the Internet and downloaded into a computer (client) via thenetwork.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A wireless communication apparatus supporting afirst wireless communication scheme and a second wireless communicationscheme, wherein minimum reception sensitivity levels of physical schemesof the first wireless communication scheme and the second wirelesscommunication scheme are equal to a first level, the apparatuscomprising: a management information base which holds an attributeindicating whether or not the apparatus operates in accordance with thesecond wireless communication scheme; a first processing unit configuredto (a) when a FALSE value is set for the attribute indicating whether ornot the apparatus operates in accordance with the second wirelesscommunication scheme, set a first power value for a maximum transmissionpower and set the first level for a carrier sense level and (b) when aTRUE value is set for the attribute indicating whether or not theapparatus operates in accordance with the second wireless communicationscheme, set a second power value lower than the first power value forthe maximum transmission power and set a second level higher than thefirst level for the carrier sense level; a second processing unitconfigured to carry out carrier sense using the carrier sense level; anda third processing unit configured to control transmission and receptionof a frame via the second processing unit, wherein: the third processingunit, upon receiving an instruction to start formation of a wirelesscommunication group from the first processing unit, and when the TRUEvalue is set for the attribute indicating whether or not the apparatusoperates in accordance with the second wireless communication scheme,generates at least one of a beacon frame and a probe response frame bothincluding a frame body which carries information indicating that anattribute of the wireless communication group is the second wirelesscommunication scheme, and a communication range of the second wirelesscommunication scheme is narrower than a communication range of the firstwireless communication scheme.
 2. The apparatus according to claim 1,wherein: the second processing unit decodes a reception signal andpasses information on the reception signal to the third processing unitwhen the reception level is equal to or greater than the carrier senselevel, and avoids decoding the reception signal when the reception levelis less than the carrier sense level, and the third processing unitpasses information on a transmission signal to the second processingunit when the reception level is less than the carrier sense level. 3.The apparatus according to claim 1, wherein the third processing unitexcludes a period for another wireless communication apparatus using thefirst wireless communication scheme to transmit a data frame, from aschedule within a beacon interval, when the TRUE value is set for theattribute indicating whether or not the apparatus operates in accordancewith the second wireless communication scheme.
 4. The apparatusaccording to claim 1, wherein the first processing unit sets acontention parameter specifying a contention window narrower than acontention window for the first wireless communication scheme when theTRUE value is set for the attribute indicating whether or not theapparatus operates in accordance with the second wireless communicationscheme.
 5. The apparatus according to claim 1, wherein the firstprocessing unit ignores a network identifier included in the receptionsignal information when the TRUE value is set for the attributeindicating whether or not the apparatus operates in accordance with thesecond wireless communication scheme.
 6. The apparatus according toclaim 1, wherein the first processing unit, upon determining to join toa wireless communication group having the attribute for the secondwireless communication scheme, rewrites the value of the attributeindicating whether or not the apparatus operates in accordance with thesecond wireless communication scheme to TRUE, sets the second powervalue for the maximum transmission power, and sets the second level forthe carrier sense level.
 7. The apparatus according to claim 1, wherein:the third processing unit, upon receiving a search instruction for awireless communication group from the first processing unit, collects atleast one of a beacon frame and a probe request frame, and notifies thefirst processing unit of information on the collected frame, and thefirst processing unit determines whether or not the apparatus can jointhe wireless communication group when the collected frame by the thirdprocessing unit carries information indicating that the attribute of thewireless communication group is the second wireless communicationscheme.
 8. The apparatus according to claim 1, wherein the thirdprocessing unit, upon receiving a search instruction for a wirelesscommunication group from the first processing unit, collects at leastone of a beacon frame and a probe request frame, and notifies the firstprocessing unit of information on the collected frame and a receptionlevel of the collected frame.
 9. The apparatus according to claim 1,further comprising an antenna which transmits and receives the frame.10. A wireless communication method performed by a wirelesscommunication apparatus supporting a first wireless communication schemeand a second wireless communication scheme, wherein minimum receptionsensitivity levels of physical schemes of the first wirelesscommunication scheme and the second wireless communication scheme areequal to a first level, and wherein the method comprises: setting, by afirst processing unit, a first power value for a maximum transmissionpower and setting the first level for a carrier sense level when a FALSEvalue is set for an attribute held by a management information base, theattribute indicating whether or not the apparatus operates in accordancewith the second wireless communication scheme; setting, by the firstprocessing unit, a second power value lower than the first power valuefor the maximum transmission power and setting a second level higherthan the first level for the carrier sense level when a TRUE value isset for the attribute indicating whether or not the apparatus operatesin accordance with the second wireless communication scheme; carryingout, by a second processing unit, carrier sense using the carrier senselevel; controlling, by a third processing unit, transmission andreception of a frame via the second processing unit; and upon receivingan instruction to start formation of a wireless communication group fromthe first processing unit, and when the TRUE value is set for theattribute indicating whether or not the apparatus operates in accordancewith the second wireless communication scheme, generating, by the thirdprocessing unit, at least one of a beacon frame and a probe responseframe both including a frame body which carries information indicatingthat an attribute of the wireless communication group is the secondwireless communication scheme, wherein a communication range of thesecond wireless communication scheme is narrower than a communicationrange of the first wireless communication scheme.
 11. A wirelesscommunication apparatus supporting a first wireless communication schemeand a second wireless communication scheme, wherein the first wirelesscommunication scheme uses a first set of modulation and coding schemes(MCSs) and the second wireless communication scheme uses a second set ofMCSs, the apparatus comprising: a first processing unit configured toset a maximum transmission power and a carrier sense level; a secondprocessing unit configured to carry out carrier sense using the carriersense level; and a third processing unit configured to controltransmission and reception of a frame via the second processing unit,wherein: the second set of MCSs corresponds to a part of the first setof MCSs, a common minimum reception sensitivity level is specified foreach of the second set of MCSs and corresponding ones of the first setof MCSs, the first processing unit sets a second level higher than afirst level for the carrier sense level and sets a second power valuelower than a first power value for the maximum transmission power, whenthe second wireless communication scheme is used, the first levelcorresponds to a lowest level among minimum reception sensitivity levelsspecified for the second set of MCSs, the third processing unit controlsan exchange of data frames using the second wireless communicationscheme in a wireless communication group having an attribute for thesecond wireless communication scheme, and a communication range of thesecond wireless communication scheme is narrower than a communicationrange of the first wireless communication scheme.
 12. The apparatusaccording to claim 11, further comprising a management information basewhich holds an attribute indicating whether or not the apparatusoperates in accordance with the second wireless communication scheme,wherein whether or not the second wireless communication scheme is usedis determined based on the attribute indicating whether or not theapparatus operates in accordance with the second wireless communicationscheme.
 13. The apparatus according to claim 12, wherein: the firstwireless communication scheme is used when a FALSE value is set for theattribute indicating whether or not the apparatus operates in accordancewith the second wireless communication scheme, the first processing unitsets the first power value for the maximum transmission power and sets athird level for the carrier sense level, when the first wirelesscommunication scheme is used, and the third level corresponds to thelowest level among the minimum reception sensitivity levels specifiedfor the first set of MCSs.
 14. The apparatus according to claim 12,wherein the attribute indicating whether or not the apparatus operatesin accordance with the second wireless communication scheme is writtento a TRUE value when the apparatus joins to the wireless communicationgroup having the attribute for the second wireless communication scheme.15. The apparatus according to claim 11, wherein when the apparatusforms a wireless communication group based on the second wirelesscommunication scheme, a management frame carries information indicatingthat an attribute of the wireless communication group is the secondwireless communication scheme.
 16. The apparatus according to claim 15,wherein when an association request frame from another wirelesscommunication apparatus does not carry information indicating that theother apparatus operates in accordance with the second wirelesscommunication scheme, a status code in an association framecorresponding to the association request frame describes a reason ofrejection that the other apparatus does not operate in accordance withthe second wireless communication scheme.
 17. The apparatus according toclaim 15, wherein: when the apparatus forms a wireless communicationgroup based on the second wireless communication scheme, a code that isnot actually indicating an MCS is defined as an MCS essential forreception in the wireless communication group, and the code is includedin a field indicating an attribute of the wireless communication groupin a management frame.
 18. The apparatus according to claim 11, wherein:the first set of MCSs includes an MCS corresponding to a first physical(PHY) scheme and an MCS corresponding to a second PHY scheme, the secondset of MCSs does not include the MCS corresponding to the first PHYscheme and includes the MCS corresponding to the second PHY scheme, anda third level corresponding to the lowest level among the minimumreception sensitivity levels specified for the first set of MCSs isequal to one of minimum reception sensitivity levels specified for thefirst PHY scheme.
 19. The apparatus according to claim 11, furthercomprising an antenna which transmits and receives the frame.
 20. Awireless communication method performed by a wireless communicationapparatus supporting a first wireless communication scheme and a secondwireless communication scheme, wherein the first wireless communicationscheme uses a first set of modulation and coding schemes (MCSs) and thesecond wireless communication scheme uses a second set of MCSs, andwherein the method comprises: setting, by a first processing unit, amaximum transmission power and a carrier sense level; carrying out, by asecond processing unit, carrier sense using the carrier sense level; andcontrolling, by a third processing unit, transmission and reception of aframe via the second processing unit, wherein: the second set of MCSscorresponds to a part of the first set of MCSs, a common minimumreception sensitivity level is specified for each of the second set ofMCSs and corresponding ones of the first set of MCSs, the firstprocessing unit sets a second level higher than a first level for thecarrier sense level and sets a second power value lower than a firstpower value for the maximum transmission power, when the second wirelesscommunication scheme is used, the first level corresponds to a lowestlevel among minimum reception sensitivity levels specified for thesecond set of MCSs, the third processing unit controls an exchange ofdata frames using the second wireless communication scheme in a wirelesscommunication group having an attribute for the second wirelesscommunication scheme, and a communication range of the second wirelesscommunication scheme is narrower than a communication range of the firstwireless communication scheme.